Begun creating a XULManager class to manage the XUL that we are injecting into the browsers chrome and ensure that it is unloaded.

Unfortunately, this currently only works with one window. I'll have to look into how Jetpack keeps widget icons in all windows. I know Jared/Gijs mentioned listening for new windows through the nsiWindowMediatorListener, but I'm unsure we'll have to make sure we're only creating one true instance of our add-ons. I'm going to try and see how Jetpack does it, and once I figure out a good method I will likely create a new class called ResourceManager that takes care of both XUL and other kinds of content.