Bug 835507 - lazy load email resources

This provides around a 200-300 ms improvement in loading the email app.

I could not find a single location inside of the MailAPI to notify the UI of a good time to lazy load the rest of the resources. Instead I decided to monitor time between paints. Currently the code will wait 1second since the last paint to load the required resources. I think this time is fairly safe for now as I don't want to delay what's required for the UI.