Make the automatic Kanban board refresh interval configurable

Currently, Kanban boards are configured with a hard coded 30 seconds refresh interval to check for board updates. If the board usage in the instance is high, and users tend to leave on for prolonged periods of time (e.g. as wallboards), boards will continuously poll Jira for updates, with each poll being a somewhat expensive operation on the Jira server resources.

For such environments, it would make sense to decrease the automatic polling interval to decrease the load on the server.

Workaround

Currently changing the automatic refresh interval is only possible by repackaging the greenhopper file with the updated refresh value:

Compile an updated greenhopper file:

1. Unpack the jira-greenhopper-plugin-*.jar plugin from $JIRAHOME/plugins/installed-plugins
2. Update 3 files includes/js/rapid/ops to change the interval to 60 seconds:
   1. Poller.js: DEFAULT_INTERVAL = 60000 (was DEFAULT INTERVAL = 30000);
   2. Poller-source.js: DEFAULT_INTERVAL=60000 (was DEFAULT INTERVAL = 30000);
   3. Poller-min.js: var r=60000 (was var r=3e4)
3. Repackage the JAR file

Replace the original file with the modified version

1. Stop Jira instance.
2. Replace the original greenhopper file in folder $JIRAHOME/plugins/installed-plugins with the modified version (take backup)
3. Remove the file $JIRAHOME/plugins/install-app-info/jira-software-application.properties (this is needed to force Jira to reload greenhopper plugin from the source)
4. Start Jira instance