Also refactor this a bit so Note contains a NoteData. I'm really not
convinced about today's abstractions, and feel I might have made this
entire thing much much worse.
This completely breaks the app, as it is part of a large refactor to
make Note loading asyncrhnous and not block. Additionally this removed
JSON serialization for Notes as that isn't something we care about any
more.
For now I've mostly tried to follow the same style guide as the flutter
repository, with many options disabled. Eventually, maybe it would make
sense to be far stricter.
It all just makes far more since when each Note has a fileName.
Though we don't save the fileName in the YAML header. It seems quite
redundant to do that.
Another advantage of this is that if we can read any file ending with a
'.md' in a git repo. It doesn't need to be named exactly how we want it,
and we will still save the details correctly.
