Let users set a default calendar for new events [with hidden buttons]

:construction: 
Continuing from: https://github.com/owncloud/calendar/pull/399

I will need @jancborchardt's help at this stage since I am not a CSS-friendly guy :). Also if @Raydiation can help me this would be perfect.
Escaping will work fine for that. Escaping just means display it and escape HTML characters. I doubt that you want to use a username to create a div in the app, correct?