Make images rotateable and made tracks editable, similar to google maps ...

Hello, 

I've made a couple of additions to this library that you might be interested in merging. 
I've added a property to OsmGpsMapImage that makes it rotatable. 
I've also added an 'editable' property to OsmGpsMapTrack that makes it behave similarly to editable polylines in the Google Maps API, and there are some new signals so that applications can determine when a track has been edited. 

Cheers, supercamel