Maps: Add FavoritesModel and remove hacky misusage of JSONArrayModel

[bplaat]

When I first created the Maps favorites panel I used the JSONArrayModel but this resulted in quite hacky ugly code. I have refactored the code now inspired by the HexEditor/AnnotationsModel.h. All is it a net code increase the new code is much more readable and maintainable.

I also moved MapsTileProviders.json to a more central location because right now with multiple users it would not work.