#97 do nothing if previous button was pressed

In AdditonalMetaDataPanel and RepresentationsPanel if store() is called,
only create a new CidsBean or edit another CidsBean, if the Next-button
was pressed.
 Closes #97: removed PreviousButtonEnabler

Removed PreviousButtonEnabler, as it is not needed anymore.
Merge branch 'feature/97-enable-back-button' into dev