Added ability to show half star rating

@hippee-lee @tsanko @kevinsproles Here is the pull request with the changes to the vnRating directive to use fontawesome. There is a related PR in the method theme to integrate it. The following bugs are fixed by this change, and can be moved to the "test" status after review.

22017 (Story)
26743 (Bug)
26744 (Bug)
26964 (Bug)