add spec for presentations controller new action
add spec for presentations controller new action

There is a bug, that the PresentationsController (or in this case the
AssetsController) creates new assets of the wrong class.

BUG: [#1909] -
https://dev.imis.uni-luebeck.de/projects/fassets/tickets/1909

RAllner/fassets_core,RAllner/fassets_core,fassets/fassets_presentations,fassets/fassets_resources,fassets/fassets_resources,fassets/fassets_presentations