Rework XMPP Date/Time related code

- Fix "packet.Time is not thread-safe" (SMACK-543)
- Update packet.Time to XEP-0202

Add SDM.supportsFeature(), since this is a pattern that repeats over and
over again in Smack. Also add abstract Manager class, that takes care of
the weak reference to Connection, as this is also a repeating pattern in
Smack.
SMACK-541 Fix of XHTMLExtensionProvider on Android
This fixes issue there on android in XHTMLExtension bodys contained "null" instead of actual xhtml tags
This happened due to difference in XPP implementation in KXmlPullParser (on Android) MXParser (in other cases)
This fix replaces usage of getText method of XPP with restoration of xhtml tags using XPP api.
Advanced Message Processing implementation (XEP-0079)

Fixes SMACK-544
SMACK-53: create VersionProvider and VersionManager

The VersionProvider is used to parse Version IQs. Integration:

	providerManager.addIQProvider("query", Version.NAMESPACE, new VersionProvider());

The VersionManager is used to reply to Version IQs. Integration:

	VersionManger.getInstanceFor(connection).setVersion(
		new Version("App Name", "1.23", "Operating System"));