ORG79 Add irrigation event support

[Alomir]

No description provided.

[dlebauer]

how do we want to test this? What should 'success' look like?

I think the following approach covers key aspects of the feature.

After reading an irrigation event:

1. Event is recognized and logged
   • irrig <0 --> error
   • printevent logs event
2. Event has intended impact
   • soilWater increases
   • if canopy irrigation:
     • immedEvap increases

It is possible that this could be done in two timesteps, one before and one the event.

This isn't comprehensive but it exceeds the 'test any feature you want to persist' expectation in the PEcAn project.