addressed issue: https://github.com/globaleaks/GlobaLeaks/issues/112
removed duplicated function
removed version 7 of DB, fixed updater
Merge branch 'master' into issues/112

Conflicts:
	globaleaks/handlers/authentication.py
	globaleaks/tests/handlers/test_authentication.py
implemented migration class for ReceiverFile, tested with db 5
Merge pull request #145 from globaleaks/issues/112

Thanks @evilaliv3! has worked well.
Merge branch 'master' into extend_expire_date

Conflicts:
	globaleaks/db/base_updater.py
	globaleaks/db/update_5_6.py