Additional change related to relevant mappings

* Remove remaining non-audit uses of `extended_*` and the actual
  extended mapping definitions themselves (in `mappings.py`)
* Adds explicit mapping definitions for missing types, to avoid
  fail-over to inefficient guesswork
* Add explicit tree-list mapping definition for remaining objects
* Remove use of `extended_*` with `with_mapping_count` in two places
* Change Audit to use `objectives` instead of
  `extended_related_objectives`
Merge pull request #1124 from reciprocity/feature/more-relevant-mapping-changes

Additional change related to relevant mappings