Open command was not using system_path to ensure user expansion.
Testrepo was using pubsdir:// instead of docsdir://. Although not
directly used in test this was misleading and incoherent.
Also fixes missing system_path in filebroker.
* only bibtex format is supported
* all tests except test_repo.py and edit test pass
* edit and update commands were not updated
* removed --format argument from export, only bibtex is supported.