Workload Characterization Scripts

[dwchang79]

Adding three new workload characterization python scripts:

1. workload-characterization.py - a script that parses omnitrace and omniperf data and analyzes the workload for performance bottlenecks.
2. plot-roofline.py - generates a HTML interactable roofline plot of the workload.
3. plot-characterization.py - generates two plots showing the CPU/GPU end-to-end timing and another showing the GPU bottlenecks.

Documentation can be found here: https://github.com/dwchang79/omniperf/blob/2.x/src/docs/Workload_Characterization_Manual.pdf