Evaluate possiblity CRAN-release

[mhermans]

Having the package on CRAN has some advantages, but requires a heavy reduction in size.

TODO:

• Evaluate whether an CRAN-release is a (longer-term) goal;
• If so, look at other data-heavy / maps-packages how they approach this.

[jwijffels]

I think we need to put all resulting objects in the inst directory but provide a way to download them from there and don't ship the data on CRAN only download it when needed.
Or maybe simplify the objects regarding shapes and only putting some smaller objects in the package.