Multi-selection in query parameter 'allowableValues' listbox for 'array' param type.

Updates the #304 behaviour - now it checks the 'array' param type instead of 'allowMultiple' attribute. 
Partly adresses also the #118. It's also associated with https://github.com/wordnik/swagger-js/pull/83, but can live without it, though.
I haven't attached the generated swagger-ui.js to the pull request.