report(category): enable all categories to show audit groups

[kdzwinel]

Enables audit grouping, previously restricted to accessibility category only, for all categories. Additionally, enables 'non applicable' group for all categories.

Before

After

Example report: http://lh-audit-grouped.bitballoon.com/

Fixes #4093

[kdzwinel]

@paulirish category-renderer.js was huuuuge. I started refactor by splitting it up into three files (perf, a11y, default). Hope that's OK? In the next step I'll move audit group support from a11y to the default renderer and (hopefully?) nuke the a11y render.

[paulirish]

sounds great

[kdzwinel]

since this is a new file we need to update https://github.com/ChromeDevTools/devtools-frontend/blob/master/front_end/audits2/module.json#L20 . Because it's missing yarn compile-devtools is currently failing.

[Edit] somehow it passes on travis, no idea what's going on

[kdzwinel]

yarn compile-devtools forced me to remove _ prefix from protected variables 😿

[kdzwinel]

@patrickhulce @paulirish as far as I remember, we agreed it to leave this as is and don't migrate to getters (this.dom -> this._dom + this.getDOM())?

[paulirish]

Took this for a spin and things look identical between master and this (except for the reportGroups in SEO)

nice work!