First social login, then setting password leads to error

[snvandoorn]

When logging in with e.g. Linked (not tested with others)
Issue 1: setting password, requires non-empty password (although no password was defined)
Issue 2: any old password is accepted, changes are accepted successfully, but not stored in the database. Password remains None
Issue 3: Then logging out and logging in, leads to 'uri_for' undefined

=> Social login can´t be used like this

[snvandoorn]

As indicated in #224, using both federated and non-federated at the same time, seems to leed to issues. At least this should be indicated in the config file.