Fixed "no such test method" error in template_tests.

Without this patch, you couldn't run an individual test
case in template_tests.

Refs #23768
Fixed #23935 -- Converted decimals to fixed point in utils.numberformat.format
Fixed #23950 -- Prevented calling deconstruct on classes in MigrationWriter.
Fixed #20392 -- Added TestCase.setUpTestData()

Each TestCase is also now wrapped in a class-wide transaction.
Refactored some tests to take advantage of refs #20392.
Fixed #23939 -- Moved session verification out of SessionAuthenticationMiddleware.

Thanks andrewbadr for the report and Carl Meyer for the review.
Added a test to verify headers set by default middleware; refs #23939.
Removed redundant numbered parameters from str.format().

Since Python 2.7 and 3.1, "{0} {1}" is equivalent to "{} {}".
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.