Redesigned Gerrit Switcher

Consolidate the two different Gerrit switcher into one. This new Gerrit
 switcher shows the currently selected Gerrit and streamlines adding a
 new instance in the form of a placeholder at the end of the list.
Add new Gerrit switcher to preferences and action bar
Fix string resource name
Update Gradle wrapper version inline with new Android studio release

PS5: Fix multiple selection problem - Let the listview itself handle
 whether items are checked or not
PS8: The placeholder row is selectable. Clicking on one of the
 EditText fields selects the row (if not already selected) and again
 enables editing. Not ideal, but it works.
PS10: Fix EditText contents being reset; sort Gerrit options in
 alphabetical order by name.

Change-Id: If5cdaa1036e6ed116d45fb7f35c607f2859587ce
Merge "Redesigned Gerrit Switcher"