Swap "Open in New Window" and "Open in New Tab" in context menus

Summary:
Since Dolphin's default behaviour became opening in new tabs rather than in new windows
(a very positive change, in my opinion), I always find myself accidentally opening folders
in new windows from the context menu. This is because in most browsers with tab workflow
(e.g. Firefox, Chromium, Falkon) the top context menu action is opening in a new tab, and
my muscle memory plays a bad trick :) I'm aware of middle-clicking, but I find it
inconvenient with my touchpad.

I suspect I'm probably not alone in that, so I think it makes sense to swap these actions
in Dolphin to match widely used apps.

Test Plan:
Open Dolphin, right click folders in the main view and in the Places panel, ensure the
actions are indeed swapped

Reviewers: VDG, ndavis, Dolphin, ngraham

Reviewed By: VDG, ndavis, Dolphin, ngraham

Subscribers: ngraham, ndavis, kfm-devel

Tags: Dolphin

Differential Revision: https://phabricator.kde.org/D27318