Move include of config.h from source to some header files

This follows dune-common!1313 (merged) to remove all the config.h includes in sources files, since they are not needed anymore. Just a few includes in header files were added for flags that are still in the config.h file but are used only in very few places.

Additionally, the optional packages are transformed in a similar way as already done in dune-common to not set any ENABLE_XYZ flat but just provide the HAVE_XYZ flag when added in cmake as a package to the target.