Themeable/Overridable output

Because we need to match the iframe that would be generated by Facebook and because Facebook does change the expected format of the iframe code occasionally I think we can stop some of the problems in this module (and prevent people from having to hack it) by outputting the ifame though the theme layer. We'll use preprocess functions to generate the variables and we'll pass this to a tpl file to actually generate the iframe code. This way users will be able to create custom preprocess functions and tpl files in thier own themes to handle changes in Facebook's API.

I've made a new branch (7.x-2.x-themeable) that implements all of this. I figure I'll give about a week for people to check it out and for some brave souls to test it before I merge it into master.