replaces DefaultExtensionElement which is now deprecated.
Also changes Stanza (and MultiMap) API so that there can be duplicate extension
elements, as this change is required for StandardExtensionElement and by
the XMPP standard.
instead of using the old baseName=smack appendix=project.name approach,
we are now going convention over configuration and renaming the
subprojects directories to the proper name.
Having a prefix is actually very helpful, because the resulting
libraries will be named like the subproject. And a core-4.0.0-rc1.jar is
not as explicit about what it actually *is* as a
smack-core-4.0.0-rc1.jar.
SMACK-265