update appMenu status only from qml side

Summary:
--add NeedsAttention status when a menu is showing, and
Passive status when the menu is not available
--remove status updates from plasmoid interface

Test Plan:
I used debug messages to confirm the status changes and
also Latte to check that dynamic background now works ok

Reviewers: #plasma, broulik

Reviewed By: #plasma, broulik

Subscribers: broulik, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D10710