[FEATURE] Admin UI for snippets

I am having issues related to template when working on the content type in the Admin UI.

When I add the Snippet Content Type, the "template" is unset:

http://sulu.lo/admin/api/nodes/530dc752-c292-4d62-b326-ea04e327dfcd?webspace=sulu_io&language=de&template=undefined&state=2

i.e. `template` is now undefined.

Is this related to anything you are doing here?