Linux: add GPU meter and process column

[cgzones]

Based on the DRM client usage stats1 add statistics for GPU time spend and percentage utilization.

Tested with i915 and amdgpu.

[BenBE]

Does this recognize/work with multi-GPU setups?

[Explorer09]

I wish the autoTitleRightAlign flag be split to a separate PR. The reason is simply I don't like the current design of the flag, and I think it deserves more discussion before introducing it into the codebase.

[kryptobolt07]

The GPU meter doesn't seem to work on my intel haswell series processor(Intel Celeron 2955u),at least in the way i expect it to,the gpu utilizationn is displayed to be zero for example when browsing the web whereas using intel's own 'intel-gpu-tools' one can notice the render engines to be in active use.