Autodetect and auto-tune GPU plugins

[ignopeverell]

With a growing number of plugins and tuning options, across 2 different proof-of-work, I'm afraid configuration is going to get complex. If most people don't get their card working or with subpar GPSs, we're more likely to lose to closed-source solutions. So we could automatically:

1. Auto detect GPUs, both how many and what type.
2. When no GPUs are detected, run the CPU miner
   1. Auto detect AVX2, and select the optimized solver.
   2. Use compat otherwise
3. For each detected GPU:
   1. Select the right plugin
   2. Configure it to run in the available amount of memory (if possible)
   3. Pre-tuned parameters for said GPU

Bonus point for helpful error messages ("can't run in 50KB memory"). Extra bonus point for a single configuration option allowing to run CuckAToo.

[yeastplume]

I'd like the configuration file to be spit out similarly to how Grin now does it, so this would be a good process to include.. do all of this configuration and then spit out the Grin.toml file pre-configured with the best known parameters, which the user can then use as a starting point for tweaks