[desktoppackage] Port to QQC2 and fix "Get New Widgets..." button text
Summary:
- Port to QQC2
- Fix "Get New Widgets..." button text
Test Plan: Try pressing Esc in the widget explorer dialog or alternatives dialog or in the panel edit mode. Also look at the "Get New Widgets..." button in the widget explorer dialog.
Reviewers: Plasma, VDG, ngraham
Reviewed By: VDG, ngraham
Subscribers: ngraham, plasma-devel, VDG, Plasma
Tags: Plasma
Maniphest Tasks: T10586
Differential Revision: https://phabricator.kde.org/D20904