MOST Update + minor cleanup

- This updates MOST to a current version.
- I think I re-integrated most of the customisations.
- Lot's of things are still broken / not working / not tested.
- don't even try to review this PR, it's to big due to the MOST update :tada: 
- better function overriding in some places by using `parent::func` instead of copying the whole function.

#### Next, I'm planning to
- update MOST (again)
- do some more changes to the model (i.e. renaming `theFile` to `file`)
- fix error messages and test the current status
- make the media-types (Image, Music, ....) class-based to allow type addition with very little work later on.