Set line length to 72 for commit messages

EditScreen and SideBySide2 both allow lines to be longer than
72 characters, but good style is to fit within 72 so that the
`git log` command line tool can insert an 8 character wide tab
at the start of each line and the message text still fits inside
of an 80 column wide terminal.

Set the line length to 72 for commit message "files".

Change-Id: I0eb2eacb1b28cc0c78eaf1e9f39852ab557d1c7c

gerrit-gwtui/src/main/java/com/google/gerrit/client/diff/PreferencesBox.ui.xml

@@ -73,6 +73,10 @@ limitations under the License.
       color: #dddd00;
     }
 
+    .box input.gwt-TextBox:disabled {
+      background-color: #cacaca;
+    }
+
     .box .gwt-ToggleButton {
       position: relative;
       height: 19px;