WIP: redesign contacts app

Work in progress on introducing a sidebar in the calendar app to provide simpler navigation through the users calendars. Also the datepicker has been restyled to improve accessibility and clean up the UI.

Refer to https://github.com/owncloud/calendar/issues/269 for earlier discussion about the new design. Let's continue here to iron out the details.

Reference screenshot:
![untitled](https://f.cloud.github.com/assets/639688/2308838/b9e9140a-a2c5-11e3-9846-ce52853b5edb.png)