Bluetooth fixes (mainly setPowered support)

This depends on an previous PR https://github.com/crosswalk-project/tizen-extensions-crosswalk/pull/188 .

The meat of this series is the setPowered() support, which basically means that we have to return an empty adapter object to JS if bluetoothd is not running, and we should be prepared to react (by retrieving the information we need) when bluetoothd appears on D-Bus.