Converted buttons to GridView + other enhancements

Converted buttons to GridView (more cleanup can be done, I think. It currently
has 3 vertical 'regions' (source select, buttons, volume) which complicate
things with several nested LinearLayouts. Can possible convert to GridLayout for
better performance).

Fixed Volume tracking while user is changing Scrollbar.
Modified print statements (including 'Output' fragment view) to convert
non-printable ISCP message characters in hexidecimal.