Fixes handle()-related strict warnings such as "Strict Standards:
Declaration of AdminPanelAction::handle() should be compatible with
Action::handle()"
Ref. #190
We don't guess the current profile anymore if the value of the profile === -1
Also sets $this->scoped for all ScopingNoticeStream inheritors, which just
like in an Action can be null if we're not scoped in any way (logged in).
lib/plugin.php now has a parent onAutoload function that finds most common
files that are used in plugins (actions, dataobjects, forms, libs etc.) if
they are put in the standardised directories ('actions', 'classes', 'forms',
'lib' and perhaps some others in the future).
