Prefs pre-sets

A proposal for simplifying the prefs interface by providing a few "pre-sets" - named preference sets - as the default interface.

Note: another design doc proposes more sweeping changes. This doc doesn't propose changing the preferences, just the interface.

Initially this would be in the web interface. Eventually the Manager should provide the same interface.

Proposed pre-sets

Max computing

Allow computing on all CPUs and GPUs, all the time. Memory limits: 90% while idle, 50% while busy

Standard

Busy: 50% CPUs, no GPU Idle: 100% of both

Energy-saver

Busy: 25% CPUs, GPU Idle: none (let the computer go into low-power mode or turn off)