Bug 908949 - Move settings DOM into indivdual files r=kaze

Moves the DOM from a comment node into a separate file. This should generally be exactly the same performance wise as what we have today. You can compare the generated HTML in: profile/webapps/settings.gaiamobile.org/application.zip to the index.html in master.

One modification was made to add support for asynchronously loaded panels as this is needed for DEBUG mode. As everything is present on the device, and the callback is fired on the same tick, there should be no performance impact.