Text: Implement automatic update logic

This fixes the dependent sequence order that we had to worry about
previously -- i.e.: we had to call ::set_style *after* both the font
and font size was set, etc. Now it is called for us internally in the
right order every time.

* Text: Remove operator = method overload; not necessary (no pointers).
* Text: Remove un-used constructor( string ).
* Text: Declare update method under private class scope.
BitmapButton, Button: Do not check for update flag

ListBox: Disable calls being made to base (parent) widget for
updating, drawing & processing (almost entirely useless).

MessageBox: Disable calls being made to base (parent) widget for
updating, drawing & processing (almost entirely useless).
BitmapButton: Fix text alignment bug

* Button: Introduce update_bounds method.
UIStyle: Introduce text alignment field

* Button: Implement use of UIStyle's text alignment field.