RSS feed of updated mods

Referencing the (already closed) issue https://github.com/KSP-CKAN/CKAN/issues/428, this is my attempt at providing a RSS feed of recently changed ckan files.

The generated RSS can surely be prettified, adding mod images and better links, but I want to see whether @AlexanderDzhoganov is o.k. with the direction I'm taking here.