Wiki login form: "remember me" is now always true
Centralized cookie handling

- Created an abstract AuthenticationService subclass to serve as superclass for
  all implementations. This class handles the setting, clearing etc. of the
  authentication cookie.
- Added a function to see if the authentication is 'externally visible', that
  is: can other websites (e.g. wiki) access the cookie?
Created a protected function to allow subclasses to handle redirecting after authentication
Updated description of the wiki URL configuration
Users logged in locally will need to re-authenticate to set the cookies

- Show login form if user is logged in but has chosen not to set cookies
  - This form has username already filled in
- Redirect to the wiki instead of looping back to authentication.
  This fixes the redirect loop when logged in locally.