Bump Postorius and Mailanclient.

Bump postorius to 1.2.3

Upgrade Postorius to 1.1.2 (maxking#209)

* Upgrade Postorius to 1.1.2

* Install django before django-mailman3

* Do not upgrade installed dependencies so that django remains compatible

Merge pull request maxking#203 from maxking/fix-inspect-docs

Update README.md

0.1.5 release with Core 3.1.1 and Postorius 1.1.1

Add code for auto-detecting database class for common cases (issue ma…

…xking#137 ) (maxking#150)

* Add code for auto-detecting database class for common cases.

* Fix unintentional space indentation instead of proper tab indentation

* Fix another left-over spaces indentation (sorry)

Upgrade Mailmanclient to latest 3.1.1

Use VERSION to build images in automated fashion

Update documentation. (maxking#54)