Runtime: warn when a trigger edge is disabled or fails

[josephjclark]

Idea: we had a problem recently where a project imported for v1 had its first edge (the trigger-job edge) was disabled. This meant that run had no steps and looked super weird in Lightning.

We should be able to:

1. warn when the trigger step edge is disabled (because this should never happen)
2. warn when the trigger edge condition returns false

In both cases the run will look pretty strange in Lightning. I think we should be able to add logging to make it a bit clearer.

Difficulty: if there's no step, is Lightning able to show the logs?