Remove old type encoding

Switch all invokers and executors over to the new typed ASTs and drop the old ValueLinearizer stuff.

@cvogt SlickBackend needs to generate TypeMapping nodes for the tables to make it work again. I've merged everything before this point into master. The first commit in this PR is the one that breaks QueryableTest.

Next up: Change the client-side interface for ProductNodes. They are Scala tuples at the moment but that limits them to 22 elements and prevents specialization. I'll try to use a different data structure that allows specialized access and scales to arbitrary lenghts. You'd only see Tuples at the outermost layer, all intermediate structures would benefit from the optimization (and the direct embedding could generate unboxed converters for case classes at compile-time).