[System tray] Modernize "Entries" category
Summary:
- Port mostly to QQC2+Kirigami FormLayout style (Don't touch the TableView since there's no QQC2 version yet)
- Use standard import names
Test Plan:
Reviewers: VDG, Plasma, ndavis
Reviewed By: VDG, ndavis
Subscribers: ndavis, plasma-devel
Tags: Plasma
Maniphest Tasks: T10586
Differential Revision: https://phabricator.kde.org/D21189