update of LiveTile Control to allow the usage ot DataTemplateSelector

update of LiveTile Control to allow the usage of DataTemplateSelector, not the perfect integration but it's working and useful.

With the current datacontext logic, Its not possible to apply a DataContentSelector. To fix that, I call manually the DataTemplateSelector after each switch on the current and next item.

It's working and allows the creation of many different ContentTemplate in a easy way.

The fix answers the issue #221