Make WP-PostRatings CSS Friendly

I've started a branch that hopefully will make WP-PostRatings more CSS friendly, meaning WordPress theme authors can style the looks of the plugin more easily through simple CSS. This means that instead of using inline images directly in the HTML, an ordered list (`<ol>`) is all the HTML there is, and the rest is taken care of with CSS and a little bit of JavaScript.

I am not complete with the refactoring; there is still a lot of work to be done with the image themes besides "stars" (which I've based my refactoring on), but I just wanted to make my branch available to you so you could have a look and perhaps help out.