Fix miscellaneous bugs and enhance colors - Version 0.6

[JulStraus]

#49 fixed some bugs for the latest release. These bugs should also be fixed in the 0.6.x version of EnergyModelsGUI as we still support it. To this end, I created the release-0.6 branch to which I will cherry-pick the corresponding commit.

[JulStraus]

Closed by #51