Need to also account for fields which may hold personally uploaded files ( #5585 )

Actually this system won't work

get selection SQL: cannot easily piggy back because we'd be joining on many tables (catalogues store entry values depending on field type)

Field hooks: Instead of defining in the hook whether to anonymise it, I added a new setting when creating fields on catalogues: "May contain personal information". That way, admins can define per-field which ones should be handled by privacy.

I did add a new method in some field hooks, privacy_field_type, to define how the privacy system should treat this field (e.g. what criteria to match against it). By default, privacy treats as an additional anonymise field unless this method returns otherwise.

Added IP address field hooks so admins can define IP addresses specifically; necessary so the privacy system can treat them as such.

Did NOT add the tables holding catalogue values to privacy hooks (at least not yet). It won't work the way I'd want it to considering values are stored separately from fields.

--- WHAT NEEDS DONE ---

* Currently v11 only matches against the catalogue entry details itself, not the values within an entry. So if a (sensitive) field contains, say, a member ID, it still won't match in privacy unless the catalogue entry itself matched. I have absolutely no idea right now how to remedy this; it is a very complex problem. Deferring to Chris on this one.