Add Targetprocess Integration

https://github.com/bugsnag/bugsnag-notification-plugins/issues/83

Also, I added an html body handlebars template as well, but I can move it into the plugin's namespace if you prefer.

![Screenshot](http://cl.ly/image/3b1l0z3k2N2Q/Image%202014-07-19%20at%202.03.32%20pm.png)