OpenPerspectiveAction: Unify, update for E4

This code fixes #324 (on the 4.x.x branch) but also works for Eclipse 3.x targets.
In addition, it replaces 3 copies of the show-or-reset-Perspective code with one that's shared.

Update OpenPerspectiveAction to allow use with both E3 and E4 (compat).
Extract PerspectiveHelper from OpenPerspectiveAction.
Move from apputil.ui to ui.util to allow use in opibuilder.
Use same code to show (or reset) perspective in OPI, alarm, scan,
databrowser, ...