refactor: Update package list to latest versions

- Also remove unused packages that are not referenced in source at all

Closes #35

requirements/base.txt

 Django>1.10, <1.11
-argparse
 django-autoslug==1.9.3
-django-floppyforms
-django-cas-client
-django-leaflet
-django-model-utils
+django-cas-client==1.2.0
 djangorestframework==3.6.2 
-distribute
-wsgiref

requirements/local.txt

 # Local development dependencies go here
 -r test.txt
-django-debug-toolbar==1.2.1
-Sphinx==1.2.2

requirements/test.txt

 # Test dependencies go here.
 -r base.txt
-coverage
+coverage==4.3.4