Prettify the way we record the TOTAL max number of active tasks on a bourreau #1565
Description
With the implementation of this PR #1559 we currently record the maximum number of active tasks within the CpuQuota records, for each users.
The same quota records also provide a default max, when the user_id field is set to blank (and in the table, it shows up properly as "(Default for all users)".
However, there another special max value, which is the allowed TOTAL number of active tasks on a Bourreau (no matter which users they belong to). That value is stored, as a convention with a record where the user ID is 'admin'. That's not intuitive, because we could think it's the limit for that particular user instead of the total for the entire Bourreau.
I'd like either that we change the convention, or that if we stick with it, at least the index, show, and edit pages somehow says 'max total' instead of 'admin', somewhere.