switch to grunt-css-flip for RTL CSS generation

BS3 commits: dec1c21e34d12493b1eb82c8659635e068d8919d
re-enable requireCamelCaseOrUpperCaseIdentifiers in JSCS & use `null` to override it for Gruntfile

BS3 commits: 310465b035353e05524a998dc29605252dc976e7