Break csslint targets.
Fix csslint errors.
Move csslint overrides in Gruntfile.js.

This works around https://github.com/gruntjs/grunt-contrib-csslint/issues/26
Update less.js to v1.7.0.
Update grunt-contib-less.
Run `grunt`.
Merge pull request #12875 from twbs/less.js

Update Less.js
Update dependencies.
Merge pull request #12864 from twbs/csslint-fix

Csslint fix