Initial import of the Text actor from Tidy

Initial import of the Text actor from Tidy

The TidyText actor is meant as a replacement for both ClutterLabel
and ClutterText.

Any text-displaying and editing actor should derive from ClutterText
and implement the various visual cues to differentiate the editable
from the non-editable state. Those visual cues usually belong to
a high-level toolkit, especially if themeing is involved.