Make the API more consistent, remove not needed auth prefix and stop
talking about advanced authentication which has been there about 10
years ago.
API changed:
- authCheck is now readCredentials
- authSetUser is now storeCredentials
- auth is now showLoginForm
- authFails is now showFailure
- storeUserCredentials is now rememberCredentials
Signed-off-by: Michal Čihař <michal@cihar.com>