Merge: Add a Dockerfile to build a full image of a Nit install

The image is based on Debian stable (jessie) with a lot of packages.
I'm not sure what is the point of such images for the end-users.

My objective was just to test a Nit installation on a fresh, full & reproductible base.

Image will be available in the docker hub: https://hub.docker.com/r/nitlang/nit/

The only tests that fails are:

* ballz_android dino_android shoot_android ui_test test_platform_android: no android
* emscripten_nodejs: no emstripten
* test_neo_args1 test_neo4j test_neo4j_batch: no neo4j
* mpi_simple: bizarre error messages
* simple_file_server: the user is root so 80 can be opened :/
* test_glsl_validation: not installed

nitunit need also to be run

Pull-Request: #2070
Reviewed-by: Jean-Philippe Caissy <jpcaissy@piji.ca>