Let plain shareJSText class use onRender and onConnect parameters

In my app, I need to listen to onConnect in order to focus the cursor in the text box when the document has loaded. As I am building a keyboard focused-app, it is a bother if the user has to click in the textarea after the "loading..." message disappears. I suppose having the callbacks make sense for a lot of use cases, not only mine, which is why I submit this pull request.  
I've never looked at coffeescript and I'm mainly a beginner, so if I've messed up something, please tell me.