Fastpath plugin doesn't start after Smack 4 update

Merged https://github.com/igniterealtime/Spark/pull/188
Fastpath plugin now loads.

I captured this today while playing around. it looks like it fails in two place. Hope this helps

Aug 05, 2016 8:50:53 PM org.jivesoftware.spark.util.log.Log debug INFO: Trying to initialize org.jivesoftware.fastpath.FastpathPlugin@1896ad9
Aug 05, 2016 8:50:53 PM org.jivesoftware.spark.util.log.Log debug INFO: Took 4 ms. to load org.jivesoftware.fastpath.FastpathPlugin@1896ad9
Aug 05, 2016 8:50:53 PM org.jivesoftware.spark.util.log.Log debug INFO: Trying to initialize org.jivesoftware.sparkimpl.plugin.viewer.PluginViewer[,0,0,0x0,invalid,layout=java.awt.GridBagLayout,alignmentX=0.0,alignmentY=0.0,border=,flags=9,maximumSize=,minimumSize=,preferredSize=]
Aug 05, 2016 8:50:53 PM org.jivesoftware.spark.util.log.Log debug INFO: Took 8 ms. to load org.jivesoftware.sparkimpl.plugin.viewer.PluginViewer,0,0,0x0,invalid,layout=java.awt.GridBagLayout,alignmentX=0.0,alignmentY=0.0,border=,flags=9,maximumSize=,minimumSize=,preferredSize=]

Exception in thread "Thread-22" java.lang.ClassCastException: org.jivesoftware.smack.packet.UnparsedIQ cannot be cast to org.jivesoftware.smackx.workgroup.packet.AgentWorkgroups
at org.jivesoftware.smackx.workgroup.agent.Agent.getWorkgroups(Agent.java:42)
at org.jivesoftware.fastpath.FastpathPlugin$2.construct(FastpathPlugin.java:117)
at org.jivesoftware.spark.util.SwingWorker.lambda$new$1(SwingWorker.java:140)
at java.lang.Thread.run(Thread.java:745)