Replace the Star ratings in the dashboard with dashicons ratings.
This also moves the ratings to only displaying full, half, or empty stars (ie. 3.0, 3.5, 4.0, no 3.7 ratings - which are rounded).
Fixes #26170


git-svn-id: https://develop.svn.wordpress.org/trunk@26380 602fd350-edb4-49c9-b593-d223f7449a82