Distributed file system - step 1

First batch of DFS related changes:

* migrateImagesToSwift.php script
* changes in CreateWiki - Favicon and Wiki wordmark will be uploaded, not just copied to ``/images``
* SwiftCloudFiles extension improved
* tweaks in SwiftFileBackend
* old TaskManager tasks removed
* add unit test for AvatarService
* add infrastructure test for uploads, moves and deletes of images

@Wikia/platform-team 

@mroszka / @lgarczewski - please review CreateWiki changes