Fixed typo in docs/ref/request-response.txt.
Refs #18586 -- Split up model_inheritance.ModelInheritanceTest
Converted recently refactored templates tests to SimpleTestCase.

These test methods don't need DB setup/teardown.

Refs #23768 and b872134b.
Documented a current limitation of multiple table annotation; refs #10060.
Fixed a typo in aggregation docs.
Fixed typo in aggregation docs link.