Move jxmppVersion and smackMinAndroidSdk to version.gradle
Update PrivacyListManager

- to use CopyOnWriteArraySet for listeners
- do not wrap instance map in sync block (getInstanceFor() is already synchronized)
- use PacketTypeFilter instead of PacketExtensionFilter
- add removeListener(PrivacyListListener)
- rework getPrivacyLists
- don't set from attribute
- remove unused getUser()
Remove PacketExtensionFilter(Class) constructor

as it's potential error prone, because most PacketExtension's don't
have a non-argument constructor required for this to work.

Also add some javadoc.
Make Filters fields final and use StringUtils