Various fixes, see description

- removed obsolete entries in QRC
- added new banner_empty.png for a more sailfish like view
- changed opacity to have the look I wanted
- tried to have similar banner size on UserPage and MeTab
- replaced search icon to fit the style of other tab icons
- fixed inbox.svg
- fixed logout
- Added credits from Openrepos description
- renewed DicksonBetaDB avatar, as old one was low-res
- added avatar placeholder image

This is how an empy banner looks like now:
http://abload.de/img/201402152201463oj1p.png
http://abload.de/img/2014021521594195jzp.png

That placeholde image could be also used while avatars of users are
loading (or error) in TweetDelegate.