Mark required controls

Created by: olvlvl

Currently, required controls cannot be easily identified. This patch marks required controls by adding an asterisk to their label. Initially, the asterisk has the color @infoText but the color is changed to @errorText or @warningText if the control group has the class .error or .warning.

I already use it for my toolkit, you can check it out here:

• http://brickrouge.org#form: Notice the "required" control in the "Required and validated" section.
• http://brickrouge.org#alerts: Notice the "required" control in with the .error class in the "Goes great with javascript" section.