* First experiment with $nvidiabar
Added nvidiabar, nvidiagraph and nvidiagauge. Using a dummy value of 50% for now until it is integrated with the nvidia value query functions.
* Implement get_nvidia_barval()
`get_nvidia_barval()` no longer returns a dummy "50%" but instead an actual value for supported arguments:
`gpuutil`, `memutil`, `membwutil`, `videoutil`,`pcieutil`, `fanlevel` and `gputemp`
Additionally, add a nvidia_display variable. This enables the $nvidia variable to be used without
out_to_x yes (X11 support still has to be built in, you just don't have to use it).
