Add support for reading md5/bcrypt passwords and updating to bcrypt

Django migration: #47 (closed)

This allow django to login users with md5/bcrypt passwords. The bcrypt hasher being on the first place, it will be used by django to update md5 passwords on login.

Format for md5 password is:

md5$$ + digest

Format for bcrypt password is:

bcrypt$$ + algo (usually 2b) + $ + rounds + $ + salt + $ + digest