hammerhead: Make proximity check opt-in

This function's behavior is annoying and can even be
a deal-breaker for new or undiscerning CM users.

Change-Id: I51e43fd2adeaab79e74541fafadac95e16b267ff
hammerhead: Disable interactive sync feature

Change-Id: Ic2cef92fa48bc8822dffb7199895ff24cb8bc0ec
hammerhead: Set volume last to avoid pops on speaker

Change-Id: I11b3d3c41f014628ac5899d3a3bfea1b7937d7bc