Shared preferences cannot be accessed from outside the SDK

The below preferences have moved to the SDK but are still needed by the product:

Preference	Mode	Use cases
blocked_total	r	Shown in icon popup
	r	Shown in day1 landing page
elemhide_debug	r/w	Checkbox in settings page1
notificationdata.downloadCount	r	Attached to uninstall URL
notifications_ignoredcategories	r/w	Checkbox in settings page
	r/w	Opt-out in icon popup
subscriptions_exceptionsurl	r	Checkbox in settings page
	r	Attach subscription parameter to uninstall URL
subscriptions_exceptionsurl_privacy2	r	Checkbox in settings page

The mode indicates whether the value of the preference is only read or also written. Either way, the product should also get notified when a value changes.

1. Write-only API exposed in #33 (closed). ↩

2. Not part of the SDK but similar to subscriptions_exceptionsurl so we may want to store them together. ↩