Bug: loading show files does not unload the old one

[LRahlff]

Was: Bug: loading scenes produces a lot of universes (in the list)

when a scene has been saved and is loaded again, it will reproduce the patch everytime, so the list will get bigger with each loading (not reproduces right now), -- needs to be tested again

loading scene overrides (in a not intuitive way) old scenes -- overcome by events

does only the universe gets loaded, but not the patchlist? -- fixed

[Doralitze]

The unification of file loading (issue #55 ) has also something to do with this. Basically we need to erase or reset the entire model prior to loading in the new show file. Issue #74 is also related to this issue.

In general, we need to implement a reset system allowing new show files to be loaded without closing and reopening the editor. While we're at it, we should also add a CLI command to load show files from the command line, enabling scripting for set-and-forget installations (for example across longer lasting events).