Added uid and model fields to discover() method
Changed therefore the ctor of SoCo()

model: preserves the model name of the speaker for later user

uid: fetch uid without performing a sonos speaker 'deep scan' with get_speaker_info

In my project i use this behavior to determine, if a new speaker is in the network (shSonos project on Github). To reduce the network activity, the deep scan is only performed on new devices and/or after an elapsed time.