Allow selecting event/category roles and registrants in attachment/folder ACLs

[ThiefMaster]

These types are already whitelisted in the models, but the AccessControlListField (which is basically a PrincipalListField) used there does not contain an option to select those types.

Unfortunately this field is still rendered using very legacy (pre-jquery) JS code. I see two options here:

• Add support for these three principal types in the legacy field. Not fun, and the code will be ugly
• Use the react-based PrincipalListField. You'd need to wrap it in a WTFPrincipalListField to integrate it in a classic form (where the initial value is loaded form a hidden field, and making any changes update the same hidden field). @Leats added two fields a while ago for the date/time pickers that make use of a similar integration, so you could have a look how it was done there.

Note: If you go for the second option (which would be the cleaner one), you will have to update the Python-WTForms PrincipalListField as well to use identifiers instead of fossils for the submitted data.

A good first step here before doing anything related to the wtforms integration would be adding support to select registration forms there (like it's done for event/category roles, ie with a hook similar to useFetchEventCategoryRoles to get the list of regforms to select etc). This could even be a separate Pull Request.