Indicate that users have left a project or been suspended

[noah-schechter]

Current If a user has left a project, there's no visual indication that they've done so. That means it's impossible to know if they'll respond to a tag (although they shouldn't be able to tag someone who isn't a current member) or if they're actually still assigned to an incident.

Proposed

1. Add some sort of flair or extra text to a user's displayed name on incidents in projects that they've left. Something like Former member or graying out their name. Still need to think on details.
2. Maybe—I'm not sure about this one—de-assign users who have left projects from those projects. This is iffy for two reasons: 1) I don't like that we're taking automatic action that is somewhat hard to explain and 2) I think a frequent/archetypal lifetime for an Atlos user at an org will end in suspension, leading to inconsistent behavior because we couldn't automatically de-assign suspended users without disrupting their use of Atlos if they're ever unsuspended.