Changing formatting of Cite drop-down for mobile/tablet interface

These changes are to accomodate the design for the mobile/tablet
version of VisualEditor which uses an icon rather than a label
for the drop-down button.

Change-Id: I1086ed4a84ae4061fcc79cc7f587657232c5d5df
Merge "Changing formatting of Cite drop-down for mobile/tablet interface"