[UX] Add a JS toggle on the modules page for core / contrib / all

As a follow up to https://github.com/backdrop/backdrop-issues/issues/494#issuecomment-6780... we should add a radio button for core / contrib / all to the top of the modules page, perhaps next to the search box. This would allow people to quickly see which contrib modules are on a site (for troubleshooting). This will probably require adding a class when the module listing is assembled.