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

README.rst

@@ -4,11 +4,10 @@ pretix
 .. image:: https://img.shields.io/pypi/v/pretix.svg
    :target: https://pypi.python.org/pypi/pretix
 
-.. image:: https://readthedocs.org/projects/pretix/badge/?version=latest
+.. image:: https://github.com/pretix/pretix/workflows/Documentation/badge.svg
    :target: https://docs.pretix.eu/en/latest/
 
-.. image:: https://travis-ci.org/pretix/pretix.svg?branch=master
-   :target: https://travis-ci.org/pretix/pretix
+.. image:: https://github.com/pretix/pretix/workflows/Tests/badge.svg
 
 .. image:: https://codecov.io/gh/pretix/pretix/branch/master/graph/badge.svg
    :target: https://codecov.io/gh/pretix/pretix