fix issue20 - cookie for default locale/repo

https://github.com/mozfr/transvision/issues/20


I've added three checkboxes ( for Source Locale,Target Locale and Repository) in the search form that allows to define the default language or repository.

All cookies are set (or unset) with javascript when the user click the checkboxes, taking the value for the language/repo chosen by the user in the dropdowns.

Cookies are retrieved with PHP that allow to set the correct locales and repo.