Allow RTM Alerts to be Disabled following the System Wide Thold Settings and allow it to respoect maintenance periods

[TheWitness]

Is your feature request related to a problem? Please describe.

The GriaAlarms plugin was designed after the Thold plugin, sharing much of it's schema and many event types. In Thold, you can disable all Tholds with the click of a mouse, and that is not present in GridAlarms.

Also, Thold supports the Maintenance plugin Main and GridAlarms does not. Please close these two feature gaps.

Describe the solution you'd like

Close the two feature gaps and inconsistencies between these two Cacti plugins.

Additional context

Makes the two tools work more consistently.