Make sure the session is unauthenticated after signing up.

Keeping the authenticated credentials (although not fully signed in) was causing some UI elements and other logic to incorrectly assume the user is signed in.
Show correct username for copy trans.

For some authentication systems, Zanata will not show the correct username when running copy trans. This fixes this issue as it will always get the currently authenticated account's username.
Merge pull request #279 from zanata/copy-trans-username

Show correct username for copy trans.
Merge pull request #277 from zanata/unauth-after-signup

Make sure the session is unauthenticated after signing up.