Change Option Group style so they are more well defined.

This matches Chosen more closely to standard HTML Selects and makes
groups easier to read.
Add type specificty to Chosen's input fields.

This helps solve problems with inhertence when dropping Chosen into
a page that also uses the type="text" level of specificty. The more
specific the CSS selector, the higher its precedence.
Merge pull request #1368 from harvesthq/css-updates

CSS Updates