[romainkieffer]

What this adds

Global Admins can now:

• Create a new exercise from the exercise picker
• Search for and view any exercise's settings, with tabs for Details (edit/archive), Team Types, Teams (with member management), and Roles
• Search for users by name or email anywhere a person needs to be picked, instead of typing raw IDs

Test plan

• just up then log in as a Global Admin
• Create a new exercise from the picker
• Open an existing exercise's settings via the new gear icon and edit its details
• Add a team type, add a team, add/remove a member
• Grant/revoke an exercise role for a user

Refs #201