#37 Make Form handler easily extensible.

[Jeremy Dorn]

Right now, all of the code for generating the HTML for the form handler is in a single function. This makes it difficult to extend the class since you have to copy this entire function.

Each input type should have its own generateHtml method in the FormHandler class. There should also be methods for wrapping form labels, wrapping inputs, wrapping input rows, validating the CAPTCHA image, generating the submit button HTML, and handling the form submission.

This makes it easy for someone to extend the plugin and only change the parts they need to make the generated form fit into their site.