make country clickable and provide country-exits only and AS-exits only links

this use-case comes from the bad-relays@ context.

When we detect exits in a given country it is useful to easily get a list of all exits in that country or in that AS.

It would be nice if you could add the following URLs/filters on the relay page:

• make country clickable put a second link next to it "(exits only)" with flag:exit
• put a "exits only" link also next to the already AS number link

thanks!