settings: Avoid NPE in NfcTrigger when device doesn't support NFC

Change-Id: I7775540a752b6f31f8c5bb51eaf20e566b4858a5
Settings: Reduce volume to safe level when headset is connected (1/2)

This is a safety feature for users who opt to raise volume above the designated
safe level while using a headset.

Currently when a user does this they are provided with no protection against
dangerously high volume levels until the next time the headset volume warning
is displayed.

This patch adds an optional feature to ensure volume is no higher than the safe
level every time a headset is connected.

Change-Id: I8ec35284a91a26511b0bc83fcc1578f38b8b4f40