use scatter plot instead of line graph in html report

[catdad]

It look much better. The screenshots from my original benchmarking tool look way better than the new grandma pages.

• fullTest and fullTest_Err as different series
• x-axis ticks should use old plot logic for determining unit
• labels for x and y axes
• add the "Download PNG" button
• cleaner code (split css and js, build at runtime)
• better legend (the one Rickshaw uses is a bit buggy, and I want better organization)
• use test name as the graph title
• add text stats report
• add colors
• x values need to be sorted (good test is the interactive custom tags example)

[catdad]

See #134, #135, #136, #138 for the work remaining in this task.

[catdad]

Beta published in v0.6.7.