v1.1: Missing methods in $admin

[webbird]

In BlackCat, $admin is an alias / accessor to CAT_Backend. Some methods that were defined in class.admin.php in WB are now in CAT_Users, for example, $admin->get_user_id(). Unfortunately, CAT_Backend does not have accessors to that methods.

Can be solved by adding __call().

[webbird]

As we will remove backward compatibility with WB and LEPTON with BC 2.0, we will leave this as-is. If someone has a specific problem with a missing method we can provide a fix for that special case.