More improvements to Pootle Fabric scripts

Instructions and a command for setting up passwordless operation, as well documentation and new commands for from-scratch deployment (as opposed to copying or upgrading existing DB) [note that there are still problems with from-scratch deployment related to South that are not addressed here, but it should work when that is fixed].

Also other miscellaneous usability and functional fixes, for missing PYTHONPATH, dump_db and documentation.