Synchronize bindingRequired

Right after PacketReader receives the 'success' stanza, indicating
successful SASL authentication, it opens a new stream. The login
process continues in another thread and checks for bindingRequired,
which may not have been set a this point yet.

bindResourceAndEstablishSession() now waits until either the binding
feature stanza is parsed or the default packet timeout occurs.
Properly sync PacketWriter's queue

by using take()/interrupt() instead of poll(). Fixes a race condition
where nextpacket() would wait for a notification that would never
arrive, because all all put(Packet) calls are still blocking.

SMACK-560
Make sendPacket throw NotConnectedException

also use XMPPConnection.sendPacket() instead of
PacketWriter.sendPacket() in XMPPTCPConnection.
Update javadoc for (get|set)CustomSSLContext()
Fix NPE in JavaxResolver

Attributes.get(String) could return 'null'. Take care of that case.