* removed some redundant functionality (e.g. Shift-F5 to change - use the console for that!)
* removed a few more leftover parts of the old music system
* savegames should not do more than resuming the music at the point of saving. (DN3D and RR only so far. Blood to be done.)
* handle music enabling/disabling in the backend, which simply knows better what to do. This was only working in the menu, so changing the CVAR had no effect.
Not tested yet!
* Added a JSON-based header to the savegames so that the unified menu can read from a common data source.
* moved loading and saving of frontend independent data to the wrapper so that support is automatic.
Since the code is extremely volatile I changed the setup so that the save is a zip file with the regular snapshot plus all added data as separate entries.
This allows compressing everything properly without savegame breaking interference.
Blood does not yet load its savegames, need to check.
