Remove the special AJAX handling to simplify the code. Now redirection
will be forced on any request that changes the subsite to re-synchronise
with the frontend.
Introduce canAccess method, and add it to alternateAccessCheck to make
sure this subsite-specific chceck is also done in situations that are
not captured by onBeforeInit.
Disables transparent subsite switch on AJAX requests.
Makes sure the subsite is appropriately set up when opening up the CMS
with a link to subsited object.