Added python 3.8 support

• Added python 3.8 support
• Removed Django support for versions prior to 2.2

Django 2.2 compatibility

Merge pull request #95 from edx/timmc/BOM-1481-unpin-django

Relax Django constraint for upgrade to 2.2

Revert out more backwards-incompatible search logic

Merge pull request #93 from edx/diana/revert=sort

Revert out sorting changes that cause edx-platform tests to fail.

Revert discovery sorting options

We are reverting this commit to unblock updates on edx-platform.

Django 2.0, 2.1, and 2.2 Compatibility

Django 2.0, 2.1, and 2.2 Compatibility

Allow discovery search results to be sorted

Merge pull request #72 from Stanford-Online/discovery-search-sort

Allow discovery search results to be sorted

Making repo oep7 and oep 18 compliant

Merge pull request #79 from edx/msingh/version_number

PROD-384: Updated version number to 1.2.3

Fix missing search excerpts when query has quotes

Merge pull request #51 from open-craft/kshitij/fix-empty-search-quotes

Fix missing search excerpts when query has quotes

Reduce set of reserved characters in Elastic searches

Remove the hyphen and double quote from the list of reserved characters
in Elastic searches, allowing more effective searches for hyphenated
terms and quoted phrases.

Tox and django 1.11 support

Includes tox support to test on different Django versions and also added the support to Django 1.11