Use filter name in URL

[LiamBrandt]

It would be useful to be able to link to the current filter applied (that black window beneath the main navigation). We could use the name of the filter (and maybe plus a date for dynamic filters) in a similar manner to how we encode popups in the URL. If a filter from the url referenced the name of a filter that doesn't exist anymore, then we could just throw that part of the URL away, or maybe give an error message to the user.