Use nsIWebProgress to watch for bad cert status warnings.

These aren't visible through the http-on-modify-response path, so we need a
different observer.

We also don't need onSecurityChange at all. onStateChange for REQUEST is
sufficient.
Refactor SSL Observatory Observer registration.

Only register observers in the event the observatory is enabled.
Cosmetic improvements to Mike's patch:

 - avoid complex indentation
 - delete the API hook that we aren't using
Add a submission parameter to say whether there was a cert warning
Merge branch 'bad-cert-observer-rebase'
Merge branch 'ssl-observatory-perf'

Conflicts:
	src/components/ssl-observatory.js
[Fontspring] Add exclusions
Merge remote-tracking branch 'origin/master'