Messaging: What and Where?

[rnugent3]

We need to establish a policy on messaging, and we're thinking about establishing that policy based on error level. If makes sense to me to present all messages with an error level of major and up, and write all other lesser errors to a .txt output file.

The error levels are here: https://github.com/HydrologicEngineeringCenter/Framework/blob/master/Base/Enumerations/ErrorLevel.cs

This approach does not currently appear to reflect messages with good news. @HenryGeorgist is there a way that we can incorporate good news messages (e.g. compute finished!) into a general policy about what level of messaging to display to the user vs to only write to text file?