Add a 'Properties' entry in the places panel context menu

Summary: Twin of D15929 for dolphin

Test Plan:
Right-click on a place or on a device in the Places panel now show a Properties entry.
Clicking on it will open its folder property.

Reviewers: Frameworks, VDG, ngraham, dfaure

Reviewed By: VDG, ngraham, dfaure

Subscribers: dfaure, elvisangelaccio, anthonyfieroni, kde-frameworks-devel

Tags: Frameworks

Differential Revision: https://phabricator.kde.org/D15973