Merge pull request #9652 from lightsofapollo/improve-error-handling

Bug 867748 - Error recovery from account settings (mostly for oauth2)
Conflicts:

	apps/calendar/index.html
	apps/calendar/js/controllers/sync.js
	apps/calendar/js/provider/caldav.js
	apps/calendar/js/service/caldav.js
	apps/calendar/js/store/account.js
	apps/calendar/js/store/calendar.js
	apps/calendar/js/views/advanced_settings.js
	apps/calendar/js/views/modify_account.js
	apps/calendar/js/views/modify_event.js
	apps/calendar/js/views/settings.js
	apps/calendar/style/modify_account_view.css
	apps/calendar/style/ui.css
	apps/calendar/test/unit/controllers/sync_test.js
	apps/calendar/test/unit/provider/caldav_test.js
	apps/calendar/test/unit/store/account_test.js
	apps/calendar/test/unit/view_test.js
	apps/calendar/test/unit/views/advanced_settings_test.js
	apps/calendar/test/unit/views/modify_event_test.js
	apps/calendar/test/unit/views/settings_test.js