.col-form-label should right align text

Created by: rexcfnghk

• Operating system and version: Windows 10
• Browser and version: Chrome 53
• Reduced test cases: http://v4-alpha.getbootstrap.com/components/forms/#using-the-grid

To keep it consistent with Bootstrap 3's horizontal form, text should be aligned to the right.

As a supporter for right-aligned labels, it is suggested that right-aligned labels have a lighter cognitive workload for users