Telephony service: add ability to always request focus for calls

Add in the ability to overlay a config value to allow for incoming calls
to always request focus no matter the current ring volume.

Change-Id: Ie1fdbf7f0783772e3a0dae9606e3b5c3ea8e1e2b
Signed-off-by: Roman Birg <roman@cyngn.com>
Merge remote-tracking branch 'cyanogen/cm-11.0' into cm-11.0