Split requirements into files

requirements/api.txt

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+djangorestframework==3.9.0
+django-rest-polymorphic==0.1.8
+

requirements/base.txt

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+certifi==2019.6.16
+chardet==3.0.4
+defusedxml==0.6.0
+Django~=2.2
+django-allauth==0.39.1
+django-autocomplete-light==3.5.1
+django-crispy-forms==1.7.2
+django-extensions==2.1.9
+django-filter==2.2.0
+django-polymorphic==2.0.3
+django-tables2==2.1.0
+docutils==0.14
+idna==2.8
+oauthlib==3.1.0
+Pillow==6.1.0
+python3-openid==3.1.0
+pytz==2019.1
+requests==2.22.0
+requests-oauthlib==1.2.0
+six==1.12.0
+sqlparse==0.3.0
+urllib3==1.25.3

requirements/cas.txt

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+django-cas-client==1.5.3
+django-cas-server==1.1.0

requirements/production.txt

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+psycopg2==2.8.4