Link exchange feature.

Hi vitich, actually this is a feature that should be carefully considered and planned.
In fact, in toplist, webmasters aren't forced to specify a page from which they will link the website, nor they are forced to display the link only on one page: they could, theoretically, display the same, plain link from all the pages of a given domain and get points for that. I do not want to force them to do so and thus reduce the functionality that toplist offers just for the purpouse of having a backlink checker.

That said, I think it would be quite cool to have a system inside toplist that, optionally but automatically, does not show on the website and in the toplist block if a given websites does not send any referrals in a configurable time-span period. Currently, it is already checked that a given website has sent "enough" (admin-configurable) hits to our website in order to be shown in the toplist page. Extending this is with the aforementioned behaviour is quite trivial.

I am open to discussion and contributions on this point, modifying the code is pretty straight-forward in this way but I don't have much time to do it.