Move from travis to gitlab-ci

.gitlab-ci.yml

+stages:
+  - test
+  - release
+
+
+.python_test:
+  stage: test
+  script:
+    - apt-get install ffmpeg
+    - python runtests.py
+
+head:
+  extends: .python_test
+  image: python:3.8
+  before_script:
+    - pip install .['testing']
+
+lts_27:
+  extends: .python_test
+  image: python:3.7
+  extends: .python_test
+  before_script:
+    - pip install wagtail~=2.7 django~=2.2 mock
+
+lts_211:
+  image: python:3.8
+  extends: .python_test
+  before_script:
+    - pip install wagtail~=2.11 django~=3.1 mock
\ No newline at end of file

.travis.yml

-language: python
-dist: xenial
-
-
-cache:
-  pip: true
-  directories:
-    - $HOME/.cache/pip
-    - $HOME/virtualenv
-
-env:
-  global:
-    - DJANGO_SETTINGS_MODULE="tests.app.settings"
-
-python:
-  - "3.5"
-  - "3.6"
-  - "3.7"
-  - "3.8"
-
-before_install:
-    - sudo add-apt-repository ppa:mc3man/xerus-media -y
-    - sudo apt-get update -qq
-    # The install of ffmpeg fails at random with 'There were unauthenticated packages' 🤷‍♂️
-    - sudo apt-get install ffmpeg --allow-unauthenticated -y
-
-install:
-  - pip install --upgrade pip wheel tox-travis
-
-
-script:
-  - tox

tox.ini

-[tox]
-skip_missing_interpreters = True
-
-envlist =
-	py{35,36,37,38}-dj{20,21}-wt24
-	py{35,36,37,38}-dj{20,21,22}-wt25
-	py{35,36,37,38}-dj{20,21,22}-wt26
-	py{35,36,37,38}-dj{20,21,22}-wt27
-	py{35,36,37,38}-dj{20,21,22}-wt28
-	py{36,37,38}-dj{30}-wt27
-	py{36,37,38}-dj{30}-wt28
-
-	# Enforce good style
-	flake8,isort
-
-[travis]
-python =
-  3.5: py35, flake8, isort
-  3.6: py36
-  3.7: py37
-  3.8: py38
-
-[base]
-deps = mock
-
-[testenv]
-commands = python runtests.py {posargs}
-pip_pre = True
-
-deps =
-	{[base]deps}
-	dj20: Django~=2.0.0
-	dj21: Django~=2.1.0
-	dj22: Django~=2.2.0
-	dj30: Django~=3.0.0
-	wt24: wagtail~=2.4.0
-	wt25: wagtail~=2.5.0
-	wt26: wagtail~=2.6.0
-	wt27: wagtail~=2.7.0
-	wt28: wagtail~=2.8.0
-
-[testenv:flake8]
-deps = flake8
-basepython = python3.5
-commands = flake8 wagtailvideos/ tests/
-
-[testenv:isort]
-usedevelop = True
-deps =
-	{[base]deps}
-	isort==4.3.4
-basepython = python3.5
-commands = isort --recursive --diff --check-only wagtailvideos/ tests/