Feat/bar chart update 46

Please review the following update.

It features changes that were suggested by Christin in the last team meeting.

I also used the update to make the bar chart rasterizer parameters variable, by moving them into the config. This required the addition of a new config namespace "representation", so some changes had to be made to the configparser package.

Additionally, I used the chance to remove some obsolete lines I came across and I added a small margin to our standard formats. This was suggested today by Sebastian, the first visually impaired person who tested our diagrams. Having no margin at all can cause the user to miss out stuff on the left page border. (e.g. bar group letters)