Merge: jwrapper generates full APIs, with contructors, getters and setters

This PR is the second part to #1578, it updates the structure of jwrapper, adds a lot of features and creates usable APIs.

Main changes:
* Rewrite of the AST visitor, type conversion and entity naming.
* Generate constructors.
* Generate getter/setters to attributes.
* Add the -p option to choose the prefix of extern class names, use the namespace by default.
* Add the -i option to scan for existing wrappers in any directory or file.
* Add the -r option to filter the target classes from a Jar archive using a regular expression.
* Add more simple tests with javap outputs.
* Add a complete (and working) example of using a custom Java collection from Nit.
* Add an example of generating an API for Android using jwrapper. This API passes nitpick, but it has not been tested as it needs to be integrated in our Android framework.

What's to do next:
* Support for primitive arrays. (This is the main reason why ~10% of the functions are disabled)
* Add static functions as top-level methods.
* Generate class hierarchy.
* Use nitls with the -i option and to add importations to the generated module.
* Fix generic params usage.

Pull-Request: #1589
Reviewed-by: Jean Privat <jean@pryen.org>
Reviewed-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>