Inject javascript into auto-generated embed page.

For now, this just ensures that the embed is always the requested size
(via love.window.setWindow). This should improve rendering performance.

The big win is being able to add new elements to the page (for example,
a loading bar, display info from conf.lua, etc.)
Clean up all of the crappy screen handling code
embed element is not flexible
Use the correct .nmf file when debugging