Allow admin users to use user/managetoken.php safely like a normal user

A stepping stone towards MDL-73088

The primary driver here is to make this page function as consistently as practical for admin users and non admin users, as well as improving the ease of auditing keys and revoking them.

So current state is:

1. generates new keys for normal users but not admin users
2. shows current services with keys but not admin users
3. shows the keys for those services but not admin users
4. allows revoking of keys  but not admin users

Proposed state is: (changes in bold)

1. generates new keys for normal users but not admin users (unchanged)
2. shows current services with keys including admin users
3. shows the redacted keys for those services including admin users
4. allows revoking of keys including admin users
5. Also show key creation date and last access date