NothingSelected method is called on correct ref

In ItemSelectedHandler in onNothingSelected block the method called on
the implicitly referenced enclosing instance. Now the reference is
explicit, so name clashes can be avoided.
Added test

Added a test to verify that an `@ItemSelect` annotated and
`onItemSelected` named method compiles.
Merge pull request #998 from WonderCsabo/997_nothingSelectedCorrectCall

NothingSelected method is called on correct ref