Bug 1624468 - Add a fast path for more gradient types in WR

Read up and install matplotlib. Write a python script to automate the conversion from CSV into SVG bar chart. Also a batch file to run the test and save out the PNG images through Wrench.

Benchmark:

benchmarks/1.out/linear-smooth.yaml.png

benchmarks/1.out/linear-hardstop.yaml.png

benchmarks/1.out/aligned-gradient.yaml.png

benchmarks/1.out/unaligned-gradient.yaml.png

First batch; five runs on wrench, each with .

benchmarks/1.out/timings.png

Second batch; five runs on wrench, each with .

benchmarks/1a.out/timings.png

Intel HD630

benchmarks/1.out_hd630/timings.png

benchmarks/1.out_hd630A/timings.png

GTX 1050

benchmarks/1.out_1050/timings.png

benchmarks/1.out_1050A/timings.png

.