Added some improvements to the files/images views in Structr UI:
Images are now listed under files. The former behaviour of not listing images in the folders and files area was inconsistent.
Images in folders are now displayed in the image gallery (was neither constistend nor handy before).
You can now extract archive files of types zip, jar, tar, cpio and dump directly in Structr.
Merge branch 'develop' of github.com:structr/structr into develop

Conflicts:
	structr-ui/src/main/resources/structr/css/main.css
	structr-ui/src/main/resources/structr/js/ge/engine.js