Ensure `ProxyListLoader` reflects current object state

* Previously, `ProxyListLoader` could emit an incomplete list of objects
  if the binding was created *after* the creation of the list item, but
  *before* the completion of the `refresh()` of the `binding.instance`
  object.  E.g., `ProxyListLoader` would initialize with the attribute
  list, and then that list would be updated with an already completed
  object.
* Now, `ProxyListLoader` will listen for events on the relevant
  attribute of the `binding.instance` object, and merge results with its
  own list.
* Also added deduplication to avoid multiple `binding.mappings` entries.
Make `with_auditors` explicitly listen on a "decoy" object

* Previously, `with_auditors` would not update when the `authorizations`
  mapping list changed; now it explicitly listens to that list to ensure
  proper refreshing.
Merge pull request #1131 from reciprocity/feature/eventual-mapping-consistency

Ensure `ProxyListLoader` reflects current object state
Merge pull request #1132 from reciprocity/feature/fix-auditor-refresh

Make `with_auditors` explicitly listen on a "decoy" object
Merge remote-tracking branch 'origin/develop' into feature/section-clause-differentiation
Add missing `DirectiveSection` definition