delete wrong test in lib
add a dropbox button which uses a dropBoxButtonablevalueObject for its implementation to the bridge
add a DeleteButtonableValueObjectTest and a DropBoxButtonableValueObjectTest which both extend from ValueObjectTestCase (with some values)
adjust DropBoxButtonable to extend von TabButtonable instead of tabopenable and buttonable (which should be backwards compatible)
add doku for entityName in Identifyable
use getDropBoxButton in DropBox (not tabButton which is included in DropBoxButton)
adjust adapter to use the dropBoxButton as its getDropBoxButton() impl
adjust tests from dropbox2 to test for the dropBoxButton acceptance
and adjust the jstester for this tests