[libtaskmanager] Add ApplicationMenu{ObjectPath,ServiceName} roles to model
Summary:
The tasks model now exposes a window's application menu object path and service name.
No update signals set up for XOrg; not sure what to listen for.
Test Plan:
See that the model has more roles and see that they're wired to the application
menu obiect path and service name on Wayland and XOrg.
Reviewers: Plasma, broulik
Reviewed By: Plasma, broulik
Subscribers: broulik, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D27959