GSoC Template Engine back-end for User Generated Documents (from Andreas)

Hi guys,

here is the (first) PR for the Template Engine back-end for User Generated Documents, from Andreas GSoC. This is just the back-end (REST service); Andreas is currently working on the UI.

I'm hoping to produce a screencast / video / blog post illustrating this over this week-end, but wanted to get this PR out so that you can start having a look at what Andreas has built for us here. Pull as-is is fine, else please rant if anything major is NOK with this...

Thanks!
Michael & Andreas