Some improvements

* Added contributors list to `composer.json` (linked to github contributors graph)
* Improved Behat context
* Fixed/Cleaned/Tested configure options handling
* add `--default` option to `install` command
@stof you are right, this will probably cause problems in the future so I'll remove this flag.

I have some plan to cover the critical code with units tests so using `-v` in Behat would not make sense.