Provide visual feedback when tapping the timer text.

This uses ColorStateList drawables.

TODO: Implement this in the App Widget. RemoteViews don't implement
setTextColor(ColorStateList). Workaround: Switch between views with
different text color drawable properties.

TODO: Merge the tenths of a second into the hh:mm:ss text field so it all
changes color together? Then the tenths will have to be the same text size.
Make the tap color feedback work in the app widget

... by flipping between 3 different views, each with its own color selector
(ColorStateList) for the text color.