Parsers handed over to IQ providers should be positioned at the IQ
child element when being invoked. Therefore we remove the wrapping
<iq> in some test XML.
Also make checkMamPrefsIQProvider() a paramterized test.
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.