FIX
1839556 -- Silent mode not really silent
Fix the dialer to not play touch tone sounds if the phone is in "silent mode".
Note we have to re-check for silent mode *every time* the user presses a
key, rather than just in onResume(), since the user can toggle silent mode
via ENDCALL-longpress (without actually leaving the current activity.)
TESTED:
- "Audible touch tones" preference off: no tones
- "Audible touch tones" preference on, silent mode off: tones play
- "Audible touch tones" preference on, silent mode ON: no tones
- Switch in and out of silent mode via ENDCALL-longpress, confirm change
takes effect immediately.