Replace Travis with GitHub actions and fix many typos (#1657)

* Create django.yml

* Fix working directory

* ..

* .

* ..

* a.

* ..

* .

* Fix typo

* Install hunspell

* maxfail

* Fix install

* .

* Reduce number of typos

* Even less typos

* Postgres debug

* Spelling fixes, yet again

* Postgres with PW

* Fix failing test

* New workflows

* Fix syntax error

* Install gettext

* Test aginst python 3.6 as well

* Clean up strategies

* Add badge, do not ignore migrations

* Use pip cache

.github/workflows/docs.yml

@@ -0,0 +1,42 @@
+name: Documentation
+
+on:
+  push:
+    branches: [ master ]
+    paths-ignore:
+      - 'src/pretix/locale/**'
+      - 'src/pretix/static/**'
+      - 'src/tests/**'
+  pull_request:
+    branches: [ master ]
+    paths-ignore:
+      - 'src/pretix/locale/**'
+      - 'src/pretix/static/**'
+      - 'src/tests/**'
+
+jobs:
+  spelling:
+    name: Spellcheck
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Python 3.8
+        uses: actions/setup-python@v1
+        with:
+          python-version: 3.8
+      - uses: actions/cache@v1
+        with:
+          path: ~/.cache/pip
+          key: ${{ runner.os }}-pip-${{ hashFiles('**/requirements.txt') }}
+          restore-keys: |
+            ${{ runner.os }}-pip-
+      - name: Install system packages
+        run: sudo apt install enchant hunspell aspell-en
+      - name: Install Dependencies
+        run: pip3 install --no-use-pep517 -Ur doc/requirements.txt
+      - name: Spellcheck docs
+        run: make spelling
+        working-directory: ./doc
+      - name:
+        run: '[ ! -s _build/spelling/output.txt ]'
+        working-directory: ./doc