Removes a ton of duplicate code, mostly related to MUCItem being
duplicated in MUCOwner and MUCAdmin, but also some other duplicate code.
Make MUC code use XmlStringBuilder.
Add ELEMENT and NAMESPACE constants to the appropriate places. Also add
"static <MUCPacketExtension> getFrom(Packet)" methods.
Make some MUC classes implement Element.
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
