Do not require the user to cast the view model.
Merge pull request #12 from rbi/dontCastViewModel

Do not require the user to cast the code behind class.
Modified Licence file
Consolidated Licence Headers

https://github.com/sialcasa/mvvmFX/issues/11
https://github.com/sialcasa/mvvmFX/issues/20
Removed unnecessary usage of the StringConverter
Switched to the usage of a selection model
CDI Example works again
Fixed Example Projects
SelectableitemList : Added getter + enhanced tests