curate Halimeh's grammar stuff.

We should curate the modules that Halimeh added here. They are quite largely duplicate. Generally, we should merge the functionality into MiKo's modules.

• grammar-type0.en.tex does not really make sense. The type of production rules seems wrong. The only additional functionality is that the non-terminals can also be called variables.
• type0-type1-...en.tex only introduces the type* symbols. They are just other verbalizations for the ones from grammar-types.en.tex I have already extended the verbalizations there.
• directderivation-derivation.en.tex is subsumed by grammar-derives.en.tex.
• contextfree-grammar.en.tex seems fully redundant. But A-rule and null rule must be merged into grammar.en.tex
• roll up all the dependencies here. These modules are either new, then they can stay where they are or need to be merged with the existing modules. Currently, the dependency cone is rather limited.