transport-xmpp: Use CopyOnWriteArraySet

instead of HashSet for stateChangeListeners to prevent a
ConcurrentModificationException.
transport-xmpp: Smack 4.1.0-alpha6, jxmpp 0.4.1-alpha1
homepage: Add report_issue.org
transport-xmpp: Set stream management resumption timeout to 5min
transport-xmpp: Add comment about upstream submission
transport-xmpp: Update proguard-project.txt
transport-xmpp: Add "XMPP Intent" feature

to send XMPP messages with an intent.