Add Jabber/XMPP integration

docs/jabber.markdown

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+Jabber/XMPP integration
+=======================
+
+You can send notifications to a Jabber room for all projects or only for specific projects.
+
+- To send notifications for all projects, go to **Settings > Integrations > Jabber**
+- To send notifications for only some projects, go to **Project settings > Integrations > Jabber**
+
+Each project can send notifications to a separate room.
+
+## Example of notification
+
+Here an example with the Jabber client Adium:
+
+![Jabber notification](http://kanboard.net/screenshots/documentation/jabber-notification.png)
+
+## Configuration
+
+![Jabber settings](http://kanboard.net/screenshots/documentation/jabber-settings.png)
+
+1. Go to **Settings > Integrations > Jabber** or **Project settings > Integrations > Jabber**
+2. **XMPP server address**: URL of the XMPP server, example: **tcp://172.28.128.3:5222**
+3. **Jabber domain**: The **"to"** attribute of the XMPP protocol, example: **example.com**
+4. **Username**: The Jabber username used by Kanboard, example: **kanboard**
+5. **Password**: The Jabber password
+6. **Jabber nickname**: The nickname used to connect to the room
+7. **Multi-user chat room**: The address of the room, example: **demo@conference.example.com**
+
+Now, Kanboard events will be sent to the Jabber conference room.
+
+## Troubleshooting
+
+- All connection errors with the XMPP server are recorded in the log files `data/debug.log` or syslog