Use jxmpp-core (0.1.0-alpha1-SNAPSHOT)

fixes also SMACK-570, since jxmpp-core's XmppStringUtil contains the fix
for SMACK-570.
Add AndroidDebugger as possible debugger

Create AbstractXMPPConnection.DEBUGGERS with possible debugger classes.
Don't remove the MUC listeners after a disconnect

keep state of XMPPConnection between disconnects.

Fixes SMACK-571
Remove javadoc references to code now in JXMPP
Removed getConfiguration from XMPPConnection and added the required methods and fixed grammar issue.
changed annotations
Merge branch 'change_getconfig_visibility' of github.com:BugsBunnyBR/Smack into change_getconfig_visibility