Add custom percentile lines to the evolution view

[mattwoodrow]

For the value I'm looking at (PAINT_BUILD_DISPLAYLIST_TIME), the vast majority of results are quick, with just the outliers representing interesting information.

For this reason, the mean and median for this probe generally are fairly useless, but the 95th percentile line shows real changes when we make improvements.

5% of paints is still a significant amount, so it would be really useful if I could look at the trends for the 99th percentile as well.

Thanks!