Django-cookieless

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- Fix breach mitigation test for Python 3 [Ed Crewe]
- Fix test settings to correct path [jonespm]
- Fix content-length and decode [C.Severance]

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- Rewrite for Python 3 and Django 2.2
- Remove xteacrypt and use cryptography

[Ed Crewe]

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- Test with latest Django 1.6.2
- Enforce session keys as strings if the session fails to save
Due to the move of the session serializer to JSON in Django 1.6

[Ed Crewe]

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- Add protection against breach attack via nonce encryption
http://breachattack.com/
- Added related test

[Chris Bailey]

- Remove line return at end of session id introduced by base64 encoding

[Ed Crewe]

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- Clean up some pylint
- Switch to base64 encoding to shorten encrypted session ids

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- Add a cookieless_signal to allow custom code to be hooked to cookieless sessions
- Pass a created flag for cookieless sessions to the signal
- Add a no_cookies marker key to cookieless sessions for the same reason
- Check automatic form rewrites to ensure that sessions are not already set manually
- Fix tests check of hidden session_id broken by extra space in hidden field
- Add post method for test class view so test posts don't throw HttpResponseNotAllowed
- Make the secret generated by settings options more unique