Feature/159 5 outputs export all graphs to png svg

https://trello.com/c/HrcXcRNQ/159-3-outputs-export-all-graphs-to-png-svg

Hint: Don't forget to make a clean build before reviewing this PR.

The only thing missing here: Graph Titles & Legend for line graphs is not displayed. I created an extra card for this. This PR is already quite a monster. https://trello.com/c/RYmdoZtF/348-when-exporting-a-figure-the-graph-title-legend-should-be-present

@Ashalynd can you figure out with Cliff what kind of priority the title & legend in the graph export has