Use pipenv for requirements

Pipfile

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+[[source]]
+url = "https://pypi.org/simple"
+verify_ssl = true
+name = "pypi"
+
+[packages]
+django = "*"
+django-model-utils = "*"
+"psycopg2" = "*"
+passlib = "*"
+celery = "*"
+redis = "*"
+gvacommon = {ref = "0.4.0", git = "https://git.dittberner.info/gnuviech/gvacommon.git"}
+requests-oauthlib = "*"
+django-allauth = "*"
+
+[dev-packages]
+coverage = "*"
+django-debug-toolbar = "*"
+sphinx = "*"
+releases = "*"
+sphinxcontrib-blockdiag = "*"
+pylama = "*"
+
+[requires]
+python_version = "3.6"