move Grunt info from README into HTML docs

Fixes #13470
Merge pull request #13531 from twbs/grunt-html-docs

move Grunt info from README into HTML docs
Update .travis.yml
Remove outdated rtl nav links
Merge pull request #13536 from Quy/master

Remove outdated rtl nav links
grunt dist
Customizer: make utilities.less inclusion mandatory

Fixes #13305.
Merge pull request #13543 from twbs/fix-13305

Customizer: make utilities.less inclusion mandatory