Adapted plugins to Nx 2.6

* changed GAs of shuffled things
* removed p-u uses, replaced with Guava
* IT deps fixed (things like pluginkit or testlm)
* removed commented out stuff from POMs, removed unneded cruft
* source imports organized, removed unused cruft

And by the way, this fixes NXCM-5297 too, as it was
the whole point: bump nexus staging client to 2.6