Missing user feedback for failing actions

Some actions do not provide user feedback when they fail.

• Profile → Updating profile settings
• Comment → Edit -> Save Comment
• Comment → Preview
• Comment → Autocompletion
• Add award emoji
• Issue → edit / new → Assignee, Milestone, Labels, Project dropdowns
• Issue sidebar → Change values (Assignee, Milestone, Due date, Labels, Weight)
• Issue sidebar → Add Todo
• Issue sidebar → Subscribe/Unsubscribe
• Repository → Branches → Delete
• Todos → Mark all as done
• Todos → Done