More samples control in Rakefile

Tidies up rake tasks around samples, gives a way to run the good samples in order rather than random.

This doesn't make things entirely consistent. You could argue it'd be nice to have a way to run either good/bad, ordered/random, list/actually_run, but I got tired :smirk: Anyone feel strongly that we need all those options?

Left the old options aliased as well.

Note also, this should wait for a merge until @wasnotrice gets #503 merged, which has some tweaks around this as well that I'll get merged over and updated since I'm meddling in the same area and don't want to block that PR.