Makes login(String user, String pass) work properly.

* Now it don't look up credentials in the usermanager framework, unless
a user is logged in
* It also gets the values (e.g. the default value for the authorization
server) from plugin.xml
Let the manager use a BioclipseException instead of a
CannotProceedException. Also removes an print out to the console.
Merge pull request #19 from bioclipse/Bug3576

Makes login(String user, String pass) work properly.