Fixed: the problem with wrong media type by error

- Added: Send broadcast message to all online users

- Added: get concurrent sessions (local or cluster wide)

Get count of unread messages in REST API plugin & added new callback plugin which call a url if user is offline

OF-938: Use correct namespace for BOSH packets

Fixed Kerberos SSO Challenge Response

2) Implemented change as per Kalchenko Alexandr (https://community.igniterealtime.org/thread/55544)

fixed MySQL Error 1093 in monitoring plugin ConversationManager & added description

Update default HZ config file to match new schema

Per community feedback here:
https://community.igniterealtime.org/thread/56508

2) fix MySQL Error 1093(can't modify the same table which is used in the SELECT part) in ConversationManager

Hazelcast 3.5.1 update

HazelcastClusterNodeInfo communication has big delay.

Using getHostString() to benefit from not attempting a reverse lookup.
Or will cause very big delay if the ip address doese not have configured
host name.

Append XMPP client namespace to outbound BOSH packets only when needed.

Update the REST API plugin to version 1.1.2

- Added: CORS to all endpoints

OF-937: OFMeet plugin should define J2EE web-app version in web.xml files

OF-937: OFMeet plugin should define J2EE web-app version in web.xml

OF-936: Plugins build task should fail on error by default.

OF-930 & OF-935 Fixes

OF-930: When a directory is defined by property, that should be used instead of a relative reference.