Consolidate mixologist generator code

It is too strict, but I can't think of a clean solution, just making it work at all :) The problem is that transformers are aware of package locations, so relative paths specified in *.mixologist.yaml appended to package path give you absolute package location, so you can work with mixins defined in multiple packages. The command line is oblivious to package locations. I think in the long run we want to get rid of binary commands and do everything via transformers. The problem is that not all environments work well with transformers yet.