WIP: Use browser.storage directly

Refs #81.

Instead of serializing all filter and subscription classes to a string in an INI format we directly use browser.storage.local.set and get.

These methods can serialize and deserialize whole objects.

This is proof of concept, in a proper version we would need to implement loading from INI storage to keep the settings of existing users.

We would also replace serialize with serialize2, because we don't need the old serialization rountines anymore.

This is mostly interesting for performance comparisions.

In my limited testing disabling and reenabling ABP correctly keeps all the subscriptions. I haven't tested filter settings yet.