Add BluetoothService to reduce resuming time after reboot

As a subclass of SystemService, BluetoothService wraps around
BluetoothManagerService to unlock Auto-enabling Bluetooth earlier by overriding
onBootPhase() and removes the need to wait for BOOT_COMPLETED message.

Bug:21705209
Change-Id: I2acc41370a750d8416e11e662e06392326741d2c