Relocation and restructuring of artifacts to app.common

Handling ressources like images and stylesheets and related utility classes

There is currently a common image project which also provides some utility functions. In addition there is also package in gui elements which provides common stylesheet loading (and maybe later stylesheet loading for apps). Possible solutions:

• Place both resources and related utilities to common-ui
• Place resources in a resource project and utilities in common-ui

-- ChristianHillbricht - 14 Sep 2018