Remove django relatives and django appconf

[dmunozv04]

Proposed changes

This PR removes django-relatives since the only function Wirecloud uses from it can be replaced with a builtin django option. It also removes django-appconf from requirements.txt since it wasn't used (a dependency uses it but not the main Wirecloud package)

Types of changes

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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

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• I have read the CONTRIBUTING doc
• I have signed the CLA
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)
• Any dependent changes have been merged and published in downstream modules

Further comments

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[coveralls]

coverage: 88.256%. first build
when pulling 1f640fe on dmunozv04:remove-django-relatives
into b197d37 on Wirecloud:develop.