Merge branch 'release/0.4.2'

Bump version, update changelog

Merge branch 'feature/flake8-all-the-things' into develop

Do use the imagecat module directly when using config variables.

Explicitely import all logging handlers

Avoid using imagecat module directly and import all used objects explicitely

Flake8 ALL the things!

Fix explicit dependencies and add mention of python-gi

Phase out build.xml and use a Makefile + setuptools instead

Add extra installable files to Debian configuration

Restructure Debian control files

Move entrypoint inside package and encapsulate logic into functions

Drop saucy support

Move version information to separate file

Merge release/0.4.1