feat(AstParser): Made the AST parser private to the scope

Replaces #758 - clean & rebased version.

- The ASTParser is no more retrieved from the injector. It has not been removed though because the former is not true for the tests,
- @mhevery in the end I didn't use your commit which makes the `FilterMap` required. I only took care to propagate the filters everywhere,
- I had to `xit` a test for Travis to be happy because of #787

I think this PR is good enough to be merged asap. I won't be able to work on it next week (on vacation) but I can polish the first two items when I'm back.