FocusedNode Selection

Introduction of fake selection for single focused nodes. This
change specifically makes the selection much nicer in appearance
for Chrome users selecting floated FocusableNodes (block images)
for example.

Added ve-ce-surface-highlights DOM element to contain styled
highlight elements.

Made adjustments to getSelectionRect to return fake selection
bounds if necessary.

Replaced old uses of showSelection with model.change().

Change-Id: I96e66567cdce6455ef3eb77568e72f23140448ff