Use EntityBareJid just as its done within PepManager. There is no need
for AsyncButOrdered in the PEP user managers, as PepManager already
takes care of that. Also the message carrying the PEP event should
always be the last parameter of the callbacks, as it is the least
important piece of information.
Introducing Smack's own XmlPullParser interface which tries to stay as
compatible as possible to XPP3. The interface is used to either wrap
StAX's XMLStreamReader if Smack is used on Java SE, and XPP3's
XmlPullParser if Smack is used on on Android.
Fixes SMACK-591.
Also introduce JUnit 5 and non-strict javadoc projects.