Make ProviderManager handle StreamFeatureProvider(s)

when a new ProviderLoader is added. This was previously missing.
Fix MUC invitationPacketListener ClassCastException

Make sure that the Packets are of type Message. To prevent:

E/AbstractXMPPConnection﹕ Exception in packet listener
    java.lang.ClassCastException: org.jivesoftware.smack.packet.Presence cannot be cast to org.jivesoftware.smack.packet.Message
            at org.jivesoftware.smackx.muc.MultiUserChatManager$2.processPacket(MultiUserChatM anager.java:124)
            at org.jivesoftware.smack.AbstractXMPPConnection.notifiyReceivedListeners(Abstract XMPPConnection.java:854)
            at org.jivesoftware.smack.AbstractXMPPConnection$ListenerNotification.run(Abstract XMPPConnection.java:876)
            at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:390)
            at java.util.concurrent.FutureTask.run(FutureTask.java:234)
            at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$201 (ScheduledThreadPoolExecutor.java:153)
            at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(Schedu ledThreadPoolExecutor.java:267)
            at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
            at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
            at java.lang.Thread.run(Thread.java:856)