into the /python subdir

This will probably break some things, as it presumes that the DD subdomain
grid views are working.

Fix and disable for all but the relevant combinations. Not yet working for
all ...

If make_...() is supposed to capture all types, it cannot be split across
several .so...

* gdt.so -> _gdt.so, to allow for magic in __init__.py
* create module structure in build tree via symlinks during cmake