Move dependency management over to bower.

DEVELOPERS OF GLCLIENT BEWARE:
This means that from now on you will have to initialise the dependencies of
GLClient by running:

    bower update
Switch to using the directive and controllers provided by jquery-file-uploader

This adds the following new features and fixes:

* Fix bug that occurs when a file upload fails: https://github.com/globaleaks/GlobaLeaks/issues/430
* Add support for uploading files via drag and drop
* More cleaner and reliable code
Remove now unneeded vendor scripts (they are now handled by bower)

DEVELOPERS: read commit 427238d for details