When sending a stream-open-like element, it depends on the actual used
transport which element is send. For example, RFC6120-style TCP uses
<stream>, whereas the Websocket binding for XMPP uses <open/>.
- De-duplicate code by moving it into AbstractXMPPConnection
- Introduce TopLevelStreamElement as superclass for all XMPP stream elements.
- Add SynchronizationPoint, ParserUtils
- Add ParserUtils
Fixes SMACK-333 and SMACK-521