Paginate recipients of a thread

[espellcaste]

This is a follow up ticket from #8508, the recipients output has the same issue where there is no way to paginate it.

So you can have any number of recipients and the BP_Messages_Thread class will return all of them.

A similar suggestion from that ticket is to add pagination support to recipients as well.

[imath]

I also agree it would be a nice improvement 😉

[imath]

We won't have time for 9.0.0 unfortunately, so let's work on it early for BP 10.0.0 :)

[espellcaste]

Closing it in favor of #8508