Old UI cleanup

[Wuzzy2]

Recently, this repository's master branch switched back to the old UI.

I suggest that before even trying to rework the UI once again, I would first make sure that the current master branch is stable (in a potentially release-worthy state), so that the master branch is a safe and clean basis to build upon. It's generally good practice the repository is always in a state that could be (at least in theory) turned immediately into a release without issue, and to put half-finished stuff into branches.

Also, VERY important, once someone DOES decide to rework the UI again, do NOT touch the master branch, create a new branch instead. When things go south, it can alwys be thrown in the garbage bin again. This will be much less painful.

This issue is a meta-issue to collect important issues of the old UI.

TODO:

• [ ] Fix #344
• [ ] Check out if README and any other information files for correctness
• [ ] Find crashes
• [ ] Find any regressions to previous released version
• [ ] Test, test, test
• [ ] Check if there are any levels in new-ui that are not contained in master. If yes, copy them over
• [ ] Check if there are fixes in existing levels in new-ui that are not contained in master. If yes, fix them also in master

Feel free to mention more things.

[Wuzzy2]

• [ ] Mark #322 and all issues before #322 as old-ui

[Wuzzy2]

OK, the label old-ui does not make sense for ALL those issue. But I know there are no new-ui issues before #322.

[Wuzzy2]

OK, README is up-to date now. And new-ui does not contain any new levels. So those two boxes can be ticked off.