FFIs shouldn't require apt install world-plus-dog

[camilleg]

Someone with no need of, say, Tcl and Ruby, shouldn't have to reverse engineer how to not build them and to exclude their dependencies.

[Infrasonics]

This should probably be realized as packages with optional features. Also means one for every major package manager.

The easy improvement for now is to make the targets for tcl/ruby/python not part of all, so who wants to build them can install the tools necessary manually for now. This at least keeps the build failures away, because e.g. with missing swig it's already working that way, but complains. See PR #13.