Add documentation with screenshots for the new review UIs

The new review UI documentation should describe the new change screen
and the new side-by-side diff screen. It provides screenshots in which
the described UI elements are highlighted so that users can easily
find the described functionality in the UI. This documentation is
based on the description of the new screens in the 'What’s new in
Gerrit 2.9' presentation that was shown at the Gerrit User Summit
2014. With this change only the commit message block and the commit
info block are documented. Follow-up changes will document the other
UI elememts. Once the new documentation is ready it should replace
new change screen introduction that is already contained in the
documentation. This guide is purely text-base and hence more difficult
to consume for users.

[1] http://storage.googleapis.com/gerrit-talks/gerrit-new-features-2.9.html

Change-Id: I5dcae829b091d405b9cd6774d63dba869b059f75
Signed-off-by: Edwin Kempin <edwin.kempin@sap.com>

Documentation/index.txt

@@ -8,6 +8,7 @@
 .. link:http://source.android.com/submit-patches/workflow[Default Android Workflow] (external)
 . Web
 .. Registering a new Gerrit account
+.. link:user-review-ui.html[Reviewing Changes]
 .. link:user-search.html[Searching Changes]
 .. link:user-notify.html[Subscribing to Email Notifications]
 . SSH

Documentation/user-review-ui.txt

@@ -0,0 +1,114 @@
+= Review UI
+
+Reviewing changes is an important task and the Gerrit Web UI provides
+many functionalities to make the review process comfortable and
+efficient. This is a guide through the review UI that explains the
+different functions and UI elements.
+
+[[change-screen]]
+== Change Screen
+
+The change screen shows the details of a single change and provides
+various actions on it.
+
+image::images/user-review-ui-change-screen.png[width=800, link="images/user-review-ui-change-screen.png"]
+
+[[commit-message]]
+=== Commit Message Block
+
+The focus of the change screen is on the commit message since this is
+the most important information about a change. The numeric change ID
+and the change status are displayed right above the commit message.
+
+image::images/user-review-ui-change-screen-commit-message.png[width=800, link="images/user-review-ui-change-screen-commit-message.png"]
+
+The commit message can be edited directly in the Web UI by clicking on
+the `Edit Message` button in the change header. This opens a drop-down
+editor box in which the commit message can be edited. Saving
+modifications of the commit message automatically creates a new patch
+set for the change. The commit message may only be edited on the
+current patch set.
+
+image::images/user-review-ui-change-screen-edit-commit-message.png[width=800, link="images/user-review-ui-change-screen-edit-commit-message.png"]
+
+The numeric change ID is a link to the change and clicking on it
+refreshes the change screen. By copying the link location you can get
+the permalink of the change.
+
+image::images/user-review-ui-change-screen-permalink.png[width=800, link="images/user-review-ui-change-screen-permalink.png"]
+
+The change status shows the state of the change:
+
+- `Needs <label>`:
++
+The change is in review and an approval on the shown label is still
+required to make the change submittable.
+
+- `Not <label>`:
++
+The change is in review and a veto vote on the shown label is
+preventing the submit.
+
+- `Not Current`:
++
+The currently viewed patch set is outdated.
++
+Please note that some operations, like voting, are not available on
+outdated patch sets, but only on the current patch set.
+
+- `Ready to Submit`:
++
+The change has all necessary approvals and may be submitted.
+
+- `Submitted, Merge Pending`:
++
+The change was submitted and was added to the merge queue.
++
+The change stays in the merge queue if it depends on a change that is
+still in review. In this case it will get automatically merged when all
+predecessor changes have been merged.
++
+This status can also mean that the change depends on an abandoned
+change or on an outdated patch set of another change. In this case you
+may want to rebase the change.
+
+- `Merged`:
++
+The change was successfully merged into the destination branch.
+
+- `Abandoned`:
++
+The change was abandoned.
+
+- `Draft`:
++
+The change is a draft that is only visible to the change owner, the
+reviewers that were explicitly added to the change, and users who have
+the link:access-control.html#category_view_drafts[View Drafts] global
+capability assigned.
+
+[[commit-info]]
+=== Commit Info Block
+
+The commit info block shows information about the commit of the
+currently viewed patch set.
+
+It displays the author and the committer as links to a list of this
+person's changes that have the same status as the currently viewed
+change.
+
+The commit ID and the link:user-changeid.html[Change-Id] are both
+displayed with a copy-to-clipboard icon that allows the ID to be copied
+into the clipboard.
+
+If a Git web browser, such as GitWeb or Gitiles, is configured, there
+is also a link to the commit in the Git web browser.
+
+image::images/user-review-ui-change-screen-commit-info.png[width=800, link="images/user-review-ui-change-screen-commit-info.png"]
+
+GERRIT
+------
+Part of link:index.html[Gerrit Code Review]
+
+SEARCHBOX
+---------