introduce the appmanager
detect icu via pkgconfig
allow receiving responses to commands in watchconnector

* the skeleton is in place for watchconnector to allow query->response
  messages. I've used call/cc style because it is impossible to make
  QBluetoothSocket synchronous (waitForReadyRead() is a no-op)

* remove watchcommands, instead create musicmanager to listen for the
  music endpoint. The other (simpler) endpoints are now listened in
  watchconnector itself. hangupAll() slot is moved to voicecallmanager.

* instead of emitting signals for each received message, listeners
  can now register for receiving messages targeted towards a given
  endpoint

* when reading from bluetoothsocket, properly handle short reads

* remove useless 'watch' namespace

* create appmanager, which mantains a database of installed apps
  (installed on the phone, that is; watch installed apps will come
  later)

* all the *Managers are now instantiated by the main Manager itself

* introduce Unpacker helper class for decoding watch messages

* implement getAppbankStatus and getAppbankUuids messages and response
  parsers

* remove file logging for now (20MB is bad for eMMC!)