Fixed build regression due to non-instantiable classes.

Defined android_bluetooth.Bluetooth*.* constants. (drydart#1)

Removed all spurious files from Git:

    $ find . -name '*.iml' -delete
    $ find . -name .idea | xargs rm -rf

Fixed a bug in android_hardware.SensorManager.registerListener().

Implemented android_hardware.Sensor#subscribe().

Implemented android_location.Location.distanceBetween().

Refactored how class/property metadata is managed.

Defined android_bluetooth.*. (drydart#1)

Updated the screenshots of the example app.

Defined android_graphics.Bitmap.