Fixes in TextView's selection.

Handles are now centered on selection corners.
Touch regions tuned, especially for the one line / last line case.
Selection mode is stopped when text is entered or modified.
New temporary assets.
New selection background color.
Using references to theme for some hard-coded colors.

Change-Id: I820ec39bb6d5a3c6598c7c34b9c8f90b848da9f3