Merge: Rationalize the usages of tools on packages

Merge: Rationalize the usages of tools on packages

In order to have autonomous packages, they should be coherent and work as is without specific user hack.

The remaining issues are:

* The absence of required source files (eg. because generated by nitcc or nitserial) that make tools unusable or reports error. The proposed solution is a new optional Makefile goal `pre-build` that has to generate the missing files. close #1720

* The requirement of arbitrary `-I` that make the tools (eg the vim plugin) unusable on the projects without prior knowledge.
The only project that use a rogue -I is `online_editor` that require things from nitc.
The proposed solution is to virtually move src to contrib/nitc as a symbolic link.
New project could then choose to import nitc (or parts of it) without being in src.

* The presence of broken nit files. Currently, only 3 broken files remain: `contrib/pep8analysis/src/parser/parser_abs.nit`, `contrib/nitc/parser/parser_abs.nit` and `contrib/nitcc/src/nitcc_lexer0.nit`. These are still open issues and will be dealt latter.

Pull-Request: #1749
Reviewed-by: Lucas Bajolet <r4pass@hotmail.com>
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>