Merge pull request #1 from Tsarev/master

specified plattform for therubyracer
Preparing for borrow receipts.
Preparing for borrow receipts. Added model.
Implemented borrowing functionality.
Manage feature plan in internal list.
Corrected app title in features.md. Added link for users on welcome page.
Changed wording from borrow to lend.
Ensure uniqueness of the media_item title in model and database.
Ensure uniqueness of the media_item title with type in model and database.
Ensure uniqueness of the media_item title with type in model and database.