Add "Open in New Window to Dolphin's places context menu

Summary:
BUG: 384352

Add an "Open in New Window" menu item to the context menu for Dolphin's places items.

Test Plan:
Tested in up-to-date KDE Neon. Works as expected:

{F3898707}

Reviewers: #dolphin, #kde_applications, dfaure, aacid, elvisangelaccio, emmanuelp, broulik

Reviewed By: #dolphin, emmanuelp, broulik

Subscribers: alexeymin, emmanuelp, broulik, sefaeyeoglu, #dolphin

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D7690