Issue #31 - Update subscriptions.xml

This is a follow up ticket to the old one on trac (6017). We needed a migration logic for new Subcriptions.xml. I used the existing method migrateFromPreviousVersion() but needed to move it (before it did nothing, except persisting the new version code). Now it is executed after the initialization of Subscriptions, which makes more sense if we want to migrate subscriptions. In addition to that, I deleted the string resources for two filter lists (malware domains and anti-adblocking walls) that are not in in the new Subscriptions.xml file anymore.