FIX N_v_Gears metrics.

* docs: Move CmdLine sect 1st and embed GUI usage.
* docs: Add (forgotten) N_vs_Gears metrics into Contribute section.
* ci, test, tkui: Do not test UI, TravisCI has no XServer.
* ci: Silence (again) filtering of README for PyPi.
** build, ci, docs: Add script to test filtering