Re-enable VisualEditor's toolbar icons on mobile.

The experience should be consistent between mobile and desktop.
We should explore re-styling these buttons to look like
Ib3c94d19231b018a509b78269001223ad0568795 in desktop as well
at a later date.

Change-Id: Ic9e4c5d12c3c75fcb195432c9155ec0a7eecac04
Merge "Re-enable VisualEditor's toolbar icons on mobile."