*8895* Include PKP PLN plugin in OJS stable

I think we're committed to our use of BagIt. Mark mentioned some meeting notes so I had a quick look - June 20 (and I think in previous weeks, but this is the last mention of it) we'd discussed moving to GPLv3 and that an OK from contributors was necessary. I believe the decision to run with BagIt was predicated on that move to GPLv3, but that hasn't happen (I don't know if we forgot or if it just wasn't feasible for 2.4.5). In any case, I'm open to suggestions here.