Fixed #17339 -- Factor out has_result into database backend.

Thanks jonash.
Fixed #18261 -- Clarified 'project root directory'
Partial revert of commit 2bf403ecbd95

Homework: write 100 times geoapp is not geogapp.
Isolate geoapp test from sitemaps app being installed or not
Trusted test skipping about gis tests running or not

With the new test discovery system, gis tests are discovered as
other tests. They should be properly skipped now when dependencies
are missing. So let's stop special casing their inclusion.
Only import gis test apps for geo-enabled DBs
Fixed #20722 -- Fixed MemcachedCache backend get_many on Python 3.
Made an aggregate test pass with spatialite backend

backends.tests.SqliteAggregationTests was failing with spatialite.
Simplified testing connection type
Added a test for the envelope() GeoQuerySet method

Refs #20718.
Avoided transaction.set_autocommit in tests.

It doesn't work as one might expect on a certain database backend where
autocommits_when_autocommit_is_off = True. That backend happens to be
popular for running tests.
Fixed #20724 -- Test failure on SQLite.

This test failure happened if the connection's NAME was set to a file
system path, and its TEST_NAME wasn't.

Thanks Claude for the report.
Fixed #20663 -- "Today" and "now" admin shortcuts.

Changed the shortcuts next to date and time intput widgets
to account for the current timezone.

Refs #7717, #14253 and #18768.
Added 1.7 release notes in TOC.
Fixed #20625 -- Chainable Manager/QuerySet methods.
Added a test to ensure that the correct set of methods from `QuerySet` are copied onto `Manager`.
Made specialized querysets inherit from custom querysets.
Removed the `base_class` attr from `QuerySet.as_manager()` to prevent TIMTOWTDI
Made changes following @timgraham suggestions.