SDK2 Additions: BluetoothConnectionService, BatteryStateService, AccelerometerService (accel_tap), Storage

Hi,
this pull request implements the following missing APIs for SDK2:
- *BluetoothConnectionService* -- [toggle on/off via F4]
- *BatteryStateService* -- [toggle plugged in/out via F5, charge / deplete with +/-]
- *AccelerometerService (accel_tap part)* -- [use x/y/z X/Y/Z to create accel_tap Events for X/Y/Z axis]
- *Storage*

For Storage the whole persist_* API is available and local persistent storage recorded in a file called
"persistent.store" in the directory that PebbleLocalSim is run from.

I tested each feature to the extent possible and I'm glad to say that a few more of the SDK2 example Watchfaces and Watchapps can now be compiled and run.