Abstract comment tones

Abstracting `.editor .comment` to `syntax-comment-color` was a no-brainer.
There may be more appropriate ways to color `.entity &.attribute-name` and
`.variable &.constant`, but maybe we'll see how it shakes out when we invert
to light colors.
Merge branch 'abstract-all-tones' into dawn

Conflicts:
	stylesheets/syntax-variables.less

Resolved by copying just the `@syntax-comment-color` definition from
abstract-all-tones into dawn and inverting.
Abstract emphasized tones
Merge branch 'abstract-all-tones' into dawn

Conflicts:
	stylesheets/syntax-variables.less
Remove direct references to base tones from base
Remove base tone references from syntax styles
Merge branch 'abstract-all-tones' into dawn