[Bug 813472] Use addon for about:support data.

About:support data is historically rarely actually submitted, which makes things hard. This change prompts the user to install an addon which will automatically fill out this important field for the user.

Currently this has a few problems revolving around the addon not being perfect and being hosted on people.mozilla.org instead of somewhere better.

This isn't ready for merge because of the problems with the addon. The code here is ready for feedback now though.

f?