Add initial Nvidia support

[ilya-zlobintsev]

This is a major PR adding support for Nvidia GPUs (with the proprietary driver) using the NVML library.

So far there are no major daemon protocol or config format changes, the existing options are applied as it makes sense. The UI also is unchanged, but it should hide the items that make no sense on nvidia (like showing compute unit count).

Currently implemented:

• Info reporting
• Frequency and fan speed readings
• Power state readings
• Power limit configuration
• Fan control with a custom curve

Missing, will be implemented later:

• Clocks configuration

Functionality not available through NVML:

• Voltage control