Adds support for setting per-term CSS styles.

Follows, as far as I can tell, the general pattern set out for the other elements of the glossary entry.  Works with Semantic MediaWiki 1.8.0.5, MediaWiki 1.21.1, and latest HEAD of Lingo and Semantic Glossary.

Uses classes instead of inline styles.

Change-Id: I9a562f10078231d69691182d9df9a093b30a835d