Renamed root ns to MvvmCross.HotTuna.Plugins.

The "Mvx" namespace clashes with the Mvx class in Cirrious.CrossCore,
breaking the build of my work projects... This version is safer, like
the 1st party plugins.
Implemented forward geocoding for Windows Phone.

And refactored the async wrapper while at it.
Oops, added disappeared file to the project.
Merge branch 'wpforwardgeocode' of https://github.com/vzsg/Mvx.Geocoder into wpforwardgeocode

Conflicts:
	Mvx.Geocoder.WindowsPhone/AsyncQueryExtension.cs