Autodetect and auto-tune GPU plugins

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.