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.
the manager must use a copy of the BlockListIQ's JID list, since it may
be the empty list which is not modifiable.
Also rename the getter methods from getJids() to getBlockedJids().
Mostly remove the helper utils. The server is required to present the
client with a consisent state of the block list and corresponding
modifications, so we should not end up with duplicate entires if we
don't check for them.
SMACK-731
