User Administration

[ingalls]

Context

Add a UI modal to allow an administrator to modify user accounts

• Change username
• Change email
• Change access level
• disable account

Only mergable after https://github.com/mapbox/Hecate/pull/210 lands

cc/ @ingalls

[ingalls]

[ingalls]

• Add Insufficient Permission dialogue to modal for Users Listing & Webhook listing, avoiding throwing an error message for 401 error
• Standardize error handling & status code additions to error object in Main.js API

[ingalls]

Tested on staging and everything seems to be in order!