Merge changes I28120e4c,I516888a5,Icd173aa6,If042a9d1,I231f1021, ...

* changes:
  floss: Change signature of DBusArg::from_dbus
  floss: Support Vec<T> in D-Bus projection property-map
  floss: Handle congestion_cb callback
  floss: Handle read_descriptor_cb, write_descriptor_cb, execute_write_cb
  floss: Handle read_characteristic_cb and write_characteristic_cb
  floss: Handle callbacks from btgatt_client_callbacks_t