#1 Separate data store and rsync upload directory

Now we save documents in two different directories:

 1. upload directory used for the synchronization process. files are deleted after being uploaded
 2. data store directory. files are kept after being uploaded.

This allows to decouple out data store (which could later change to a database, for example) from the synchronization process (rsync, needs files).
By deleting uploaded files we also reduce the size of diffs sent by rsync.