Add Operational Event Entity

[StephenOTT]

Need for a "Operational Event" Entity. (possibility based on or related to Calendar Events?).

A Operational Event is used for operations to mark points in time that are important to be remembered later on when reviewing statistics and other questions about "why does the data look the way it does".

Example:

1. Every spring a local government will undergo "Road Repair"/"Fixing Potholes" operations. At this point it is common for a local gov to stop taking additional service requests. Therefore we will see a change in the data pattern: where new SRs drop to ~zero. When we run stats later on, we want to ensure that we are aware of these changes in the data patterns. For yearly patterns it is likely known. But for one-time events (like a major protest over several days, emergency event, etc) we can easily forget when these events took place and their impacts on the statistics.

Typical Operational Event Data would be:

1. Date
2. Description
3. Tags