Move some code to platform

[laeubi]

@tjwatson I think things have become more easier today with git(hub) so If you feel something should be moved out of equinox let me know we already have moved things around in the past without much hassle.

Besides org.eclipse.equinox.bidi and org.eclipse.equinox.security.ui I don't think we have a good existing home to move things to. For these two I would suggest they move to platform. But I'm not sure it is worth your time to make this move. I wont complain if you choose to spend time on it though.

p2 is already in its own github repo, but it contributes to the Equinox SDK and p2 has UI components also so it would pull in a bunch of stuff from platform anyway to make it fully resolvable.

Originally posted by @tjwatson in #589 (comment)