Allow the Tracking of current outage events

[ryanmerolle]

Is your feature request related to a problem? Please describe.
Currently outage events can be tracked similar to maintenance events, but not always do they have an end time but an optional Estimated Time to Repair.

Describe the solution you'd like
Options:

• Introduce a new model with all the same relationships to models that CircuitMaintenance can relate to (likely creating an abstract model both can draw on)
• Update Maintenance model to allow for:
  • a new way to signify the notice as an emergency or outage event
  • optional end time if the maintenance type (new field) is set to outage or emergency
  • Add an estimated time to repair if the type is set to emergency/outage

Describe alternatives you've considered
Make another plugin.

Additional context
Add any other context or screenshots about the feature request here.