Initialize representation's scalar bar actors.

Neither vertex nor edge scalar bar widgets were using lookup tables
provided by the view theme. Nor were their titles being set.
We also have the representation provide access to the scalar bar
widgets so that their locations can be set programatically.

Change-Id: I1184632cebb7b637344b3ed209f857f615384146
Merge topic 'broken-view-scalar-bar' into master

8ee7cfbf Initialize representation's scalar bar actors.