[Feature Request] Get new sites from peer exchange method.

[tangdou1]

I found in the code that the pex method is only used to increase the number of peers of serving site.
While it is also possible to find new sites which is not serving in my own peer but serving in all connected peers.
（Maybe I am wrong in reading the source code and this function has been released）

[purplesyringa]

This hasn't been implemented yet. The idea looks promising though, I have some implementation ideas too. @HelloZeroNet I think I can implement this, are you okay with the idea itself?

[HelloZeroNet]

It would not be hard to implement, but not sure if it's necessary, since we have shared trackers which is similar to this.

[tangdou1]

tracker can be easily banned. Also the number of trackers is small the number of active users.