[feature] - support dropping launchers from outside like the taskmanager

[psifidotos]

Hello, very beautiful plasmoid and it is something that was missing from Latte ecosystem also.

The feature is self explanatory, because I am not that fond of adding the launchers from the settings window, I propose an alternative. The user could be able to drag them from its app launcher and drop them at the popup launcher.

[dfaust]

That's a good idea. But I'm not sure when I'll have the time for that. Unfortunately there is extremely little documentation on writing plasmoids, so things like these can take a lot of time.