Build: Add CSSLint for CSS validation

Turn off all failing tests to start
CSSLint: Remove units from zero values
CSSLint: Cleanup empty selectors

Mostly caused by how Sass treats comment blocks inside selectors.
"empty-selector" rule can be turned on after Magnific-popup PR 303
CSSLint: Text-indent RTL fixes

Twitter SCSS wasn't being imported but also had -9999px text-indent.
CSSLint: display inline ignores float and margins

https://github.com/stubbornella/csslint/wiki/Require-properties-appropriate-for-display
CSSLint: Don't use regex selectors

Performance is bad, so replaced with an extension since the "brdr"
classes were the only one using them.
Merge pull request #3863 from nschonni/v4-add-csslint-to-build

V4 add csslint to build