Move CSS for pets that have been raised into mounts from stable.jade to inventory.styl

`stable.jade`
* Added a class of `.pet-evolved` for pets that have been raised into mounts. 
* Removed inline styles

`inventory.styl > .pet-evolved`
* Added styles from `stable.jade`
* Changed the opacity method for IE as Stylus was choking on `filter: alpha(opacity=10)`. Since this method targets IE7, it seemed obsolete anyway
* I didn’t understand the comment “if this could be changed to the opacity talked about? can't figure it out”, so I kept it, but moved it from `stable.jade` to keep it with the CSS.

UUID:1322727e-9911-4ad4-aea9-a5ebd8cba826
User: Pixel