Show a side menu on all 'admin' pages

Whenever an 'admin' route is detected, show gr-admin-view, with a
sub-view in the main content area. This allows a single
sidebar to be shared amongst all admin pages, and allow easy navigation
between sections.

The 'more' dropdown is now just a link that goes to the first admin
item (project list). Design was concerned that there were too many ways
to navigate between sections otherwise.

Future changes will include:
- Mobile consideration
- Dynamically Updating project/group specific pages when viewing a
  project or a group

Change-Id: I3d8622f5bf960235c1feddb602cc7b3edfabd998

polygerrit-ui/app/styles/gr-menu-page-styles.html

@@ -24,6 +24,12 @@ limitations under the License.
         margin: 2em auto;
         max-width: 46em;
       }
+      main.table {
+        margin-top: 0;
+        margin-right: 0;
+        margin-left: 14em;
+        max-width: none;
+      }
       h2.edited:after {
         color: #444;
         content: ' *';
@@ -36,6 +42,9 @@ limitations under the License.
         main {
           margin: 2em 0 2em 15em;
         }
+        main.table {
+          margin-left: 14em;
+        }
       }
       @media only screen and (max-width: 53em) {
         .loading {
@@ -44,6 +53,9 @@ limitations under the License.
         main {
           margin: 2em 1em;
         }
+        main.table {
+          margin: 0;
+        }
       }
     </style>
   </template>