Test django 11 on py36

Allow tox to run django based on env choice

Don't complain about missing interpreters

.gitlab-ci.yml

+stages:
+  - initial_testing
+  - django11
+  - docs
+
 variables:
   POSTGRES_DB: thalia
   POSTGRES_USER: postgres
@@ -5,6 +10,7 @@ variables:
   CI_DEPS: psycopg2
 
 pep8:
+  stage: initial_testing
   image: python:3.4
   before_script:
     - export PIP_CACHE_DIR="pip-cache"
@@ -23,23 +29,52 @@ pep8:
     - apt-get update
     - apt-get install -y ghostscript  # required for Thabloid's tests
   script:
-    - tox -e $PYTHON_VERSION
+    - tox -e ${PYTHON_VERSION}-${DJANGO_VERSION}
     - cd website
     - coverage report
 
-python34:
+python34-django10:
+  <<: *djangotest
+  stage: initial_testing
+  image: python:3.4
+  variables:
+    PYTHON_VERSION: py34
+    DJANGO_VERSION: django10
+
+python35-django10:
+  <<: *djangotest
+  image: python:3.5
+  stage: initial_testing
+  variables:
+    PYTHON_VERSION: py35
+    DJANGO_VERSION: django10
+
+python34-django11:
   <<: *djangotest
+  stage: django11
   image: python:3.4
   variables:
     PYTHON_VERSION: py34
+    DJANGO_VERSION: django11
 
-python35:
+python35-django11:
   <<: *djangotest
+  stage: django11
   image: python:3.5
   variables:
     PYTHON_VERSION: py35
+    DJANGO_VERSION: django11
+
+python36-django11:
+  <<: *djangotest
+  stage: django11
+  image: python:3.6
+  variables:
+    PYTHON_VERSION: py36
+    DJANGO_VERSION: django11
 
 docs:
+  stage: docs
   image: python:3.5
   before_script:
     # install django deps

tox.ini

 [tox]
-envlist = flake8,py34,py35
+envlist = flake8, {py34,py35}-django{10,11}, py36-django11
 skipsdist = True
+skip_missing_interpreters = True
 
 [testenv]
 changedir={toxinidir}/website
 commands =
+    cp {toxinidir}/requirements.txt {envbindir}/reqtemp.txt
+    sed -i /Django>=.*/d {envbindir}/reqtemp.txt
+    pip install -r{envbindir}/reqtemp.txt
     pipconflictchecker  # if this fails, use pipdeptree to debug
     python manage.py check
     python manage.py templatecheck --project-only
     python manage.py makemigrations --no-input --check --dry-run
     python -Wall -mcoverage run --branch --source '.' manage.py test
 deps = 
-    -r{toxinidir}/requirements.txt
     coverage
     pip-conflict-checker
+    django10: django>=1.10,<1.11
+    django11: django>=1.11b1,<1.12
     {env:CI_DEPS:}
 
 passenv = GITLAB_CI
+whitelist_externals=
+    sed
+    cp
 
 [flake8]
 exclude = */migrations/*, */urls.py, .ropeproject