Added release notes for 1.6.

Since 1.5 is feature-frozen, we need them to document new features.
Fixed #17744 -- Reset default file storage with setting_changed signal
Prevented file_upload tests to leave files behind

Refs #19206.
Fixed #19174 -- Fixed capitalization errors in LANG_INFO

Thanks waldeinburg for the report.
Fixed #16671 - Added a tutorial on reuseable apps

Thank-you Katie Miller and Ben Sturmfels for the initial draft,
as well as Russ and Carl for the reviews.
The timeout variable wasn't defined, which was a little confusing.
Merge pull request #481 from epicserve/testing_docs_update

Added timeout local to selenium sample test

The timeout variable wasn't defined, which was a little confusing.
Removed dupe_avoidance from sql/query and sql/compiler.py

The dupe avoidance logic was removed as it doesn't seem to do anything,
it is complicated, and it has nearly zero documentation.

The removal of dupe_avoidance allowed for refactoring of both the
implementation and signature of Query.join(). This refactoring cascades
again to some other parts. The most significant of them is the changes
in qs.combine(), and compiler.select_related_descent().
Fixed #17083 -- Allowed sessions to use non-default cache.
Fixed #19070 -- urlize filter no longer raises exceptions on 2.7

Thanks to claudep for the patch.
Add `form` to formwizard context (includes tests)
minor fix (+'.' to end of line)
Fixed #19216 - Switched to user level installation in apps tutorial.

Thanks Nick Coghlan for the suggestion.
Fixed #19179 - Added mention of NamedUrlSessionWizard and NamedUrlCookieWizard; thanks Tom for the report.
Fixed #16678 -- Wrote tests for contrib.redirects app

Thanks Julien Phalip for the report.
Added WizardView.file_storage exception message and docs

Thanks Danilo Bargen for the patch.
Fixed #19225 -- Typo in shortcuts docs.

Thanks SunPowered for the report.
Documented minimal python 3.2 version.
Fixed a regression in gis introduced by Query.select_fields removal
Fixed #15361 - Documented performance considerations for QuerySet.get()

Thanks mmcnickle for the patch.