Added description of the parameters
Added a dummy user and group provider to test preauthentication without
dependencies to other plugins.
Update classpath and gitignore
Improved readme.
Update sonar-plugin-api to 4.3.1
Made sure that AutomaticLoginFilter only redirects when no session
exists, and creates one if there is none, to avoid redirect loops.
Only PreAuthFilter checks if there is a preauthenticated user.
Make controller nil safe
PreAuthAuthenticator must not allow empty usernames
Minor cleanups