SideBySide2: Support linking directly to a line of code or comment

Using "@nnn" as a suffix on the URL token will open the file at
the given line on the B (right) side of the file. "@aNNN" can be
used to open the file relative to the line NNN on the A (left) side.

In the History section of ChangeScreen2 hyperlink each line number
to the line that comment appears on.

Bug: issue 348
Change-Id: I37de37d63d5deb6dc38f040e7e9b2bf5b09ef909

gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/DisplaySide.java

@@ -15,6 +15,6 @@
 package com.google.gerrit.client.diff;
 
 /** Enum representing the side on a side-by-side view */
-enum DisplaySide {
+public enum DisplaySide {
   A, B
 }