808 sort PURL by version scheme

[rejzzzz]

Fixes #808

• added univers sorting library
• kept natsort as fallback

now it should have 1.6.0 < 1.53.0

Signed-off-by: Rejwanul Hoque hoquerejwanulrh@gmail.com

[rejzzzz]

TESTS:

• added 5 unit tests (with 18 test cases) in SortVersionTestCase inside test_models.py

python3 manage_purldb.py test packagedb.tests.test_models.SortVersionTestCase --settings=purldb_project.settings
Found 5 test(s).
Creating test database for alias 'default'...

Compute license_detections for 0 resources.
Updating DB objects...
System check identified no issues (0 silenced).
.....
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Ran 5 tests in 2.543s

OK
Destroying test database for alias 'default'...

• added 3 integration tests in test_sort_version_integration.py

python3 manage_purldb.py test packagedb.tests.test_models.SortVersionTestCase packagedb.tests.test_sort_version_integration.SortVersionIntegrationTestCase --settings=purldb_project.settings
Found 8 test(s).
Creating test database for alias 'default'...

Compute license_detections for 0 resources.
Updating DB objects...
System check identified no issues (0 silenced).
........
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Ran 8 tests in 4.004s

OK
Destroying test database for alias 'default'...