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.
- consolidated the 3 identical S_OpenAudio implementations. The replacement code is disabled for the time being because it needs a rewrite. The replacement logic is uses is a bit too volatile.
- removed the old GRP scan code.