OC Avatars

## OC Avatars
Here they are.

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TODO:
 - [x] Use custom default avatars @kabum 
 - [x] Finish designing @jancborchardt 
 - [x] Fix unittests (encryption and local avatars @schiesbn @FlorinPeter)
 - [x] Fix unittests (the rest)
 - [x] Get rid of all `TODO`s
 - [x] Make avatar.php RESTful
 - [x] Have a better way of error-notification than interruptive alerts
  * Image is not square; Fixed
  * Image is not valid/png/jpeg; Fixed
 - [x] Include Jcrop owncloud/3rdparty#49
 - [x] Have a controller instead of avatar.php

Review the code!