Use Eyeball for semantic validation

[clange]

@np00, once syntactic validation (#9, #10) works I would also like us to implement some level of semantic validation. First a bit of generic semantic validation, later maybe extending it to MobiVoc-specific rules and "code styles".

Jena's Eyeball looks suitable for this. On the generic level I have used it before, but it is also highly configurable beyond that.

Eyeball has a comprehensive command-line frontend, but if the output becomes too complex to process, we can also invoke Eyeball from the Java side.

I told @lavdim about it, too, but will for now assign all validation-related issues to you.