[experiments] Refactor plotting

The old implementation did too many things on behalf of
the user like calling the online plotform to download
the plotter requested if missing with no way to disable
that behaviour. This would block the development of new
plotters since they would not be found online and the
command would end early.

Fixes #38
4 jobs for 38_improve_offline_plot_support in 9 minutes and 32 seconds (queued for 2 seconds)