fixed copyright notices (GNU Mailman => Postorius)

- removed some more mailmanweb remains ...

- capped line lengths
- removed some unnecessary files
- added installation instructions
- updated copyright dates

* added copy of the GPL ...

* added NEWS.rst
* added copyright text to setup.py
* small style changes
* added confirmation dialogue when deleting list
* user profile as table
* added "no todo items" text to todos
* added dependency check contributed by Daniel Mizyrycki
* small markup changes (buttons etc)