Superuser user listing and profile management

[Prakhar896]

This PR introduces the following changes:

• User management page at /admin/iam that can be accessed from admin console (/admin). User must be a superuser.
• Profile.jsx has been re-purposed to also be useful to superusers. Superusers viewing regular user's profiles is at /profile/:userID, while regular own profile viewing is at /profile. Both routes use the Profile.jsx page.
• For superusers viewing regular user profiles, buttons for invalidating user session, resetting password and deleting account are also provided.
• Superusers are also permitted to delete regular user avatars, but not replace them.
• Sidebar now renders a nice little pink badge if the logged in user is an admin
• Superuser-privileged pages are wrapped in a new <SuperuserLayout />, except for Profile.jsx which carries out security logic manually.