Only login if not already authenticated

Calling login here calls identity.request to be called, which in turn
eventually results in the onlogin callback running.

The onlogin callback is not currently idempotent (and it isn't trivial
to make it so) so this results in errors being thrown by Annotator.

Fixes #1611.
tests/js: Normalise controller namespace and names

These names were updated in scripts/controllers.coffee but not here.
Merge pull request #1640 from hypothesis/1611-fix-double-login

Only login if not already authenticated