Move to classic unconfined snap package

[LyzardKing]

As discussed this PR adds the unconfined snap package.
The package will be larger since it must include the qt5 libraries needed by the ui.
It should work with most (if not all) external packages, since it has full access to the system (as if it were installed via apt)

[LyzardKing]

@JanWielemaker This PR makes the install larger, since it is adding the qt libs needed for the UI interface. We can then see if it is possible to reduce the size after it has been tested. If you want to add it to the edge channel it could be useful for testing purposes.

[JanWielemaker]

I'm still in doubt about this. I found recently that the snap has about 1,000 weekly users. That is not a lot, but enough to justify it. Thanks! The main problem with the snap is linking foreign extensions against it. I think we had one complaint on Discourse, right? Does this justify a bigger snap and (as I understand correctly) a not-preferred unconfined snap?

[LyzardKing]

I think (but I'd need a better way to test it) that the unconfined snap should have less problems in linking foreign extensions.
If there's a good way to test this it might be good to give it a go.
It would also be interesting to figure out what is needed for the integration in a confined snap, but I'm less confident in the feasability of that last part..