Fix #373 - Enable Filter dropdown

Bundles in a refactor of how we compute the Issues url and params and gets rid of jQuery.deparam which we no longer need.

I removed the "View issues assigned to me" option from the design mockup because we don't really display what issues are assigned or provide tool to assign issues. So if we do that in the future, we can add it.

With this added, we should probably re-open https://github.com/webcompat/webcompat.com/issues/416 because I think I changed my mind how that should work. Will put thoughts there.