Enable/disable task fail/aborted sent to New Relic, per reload task

[mountaindude]

Similar to how alert emails can be enabled/disabled per reload task, the same level of control should be available for failed/aborted events sent to New Relic.

Use a custom property to control which NR account the reload failed/aborted event/log should be sent to.
Note: This assumes that the values of the custom property are the same as the New Relic account names defined in Butler's config file. Might be good to verify this during Butler startup and warn if things don't match.

Should also exist a default option, i.e. to send events/logs for tasks where the custom property is not set to one or more New Relic accounts.