In Webhooks, give errors human-readable labels and show reminder text for "Silent Mode"
Currently, we report "hook" and "silent", which are raw internal codes.
Instead, report human-readable labels so the user gets a better hint about what's going on ("In Silent Mode").
Also, render a "hey, you're in silent mode so none of this will work" reminder banner in this UI.
- New warning banner.
- Table has more human-readable text ("In Silent Mode").
Reviewed By: amckinley
Differential Revision: https://secure.phabricator.com/D19929