Added function export to CSV to graphs

I added an icon to the graphs to export the graph to CSV. The icon needs to be replaced by a better looking icon. I used an existing icon from folder media.
From time to time it could be helpful to export the current graph to a CSV for further processing. The same can be done for JSON and XML format, too. But this might be to many icons.
To solve this one idea could be to add a parameter to the config file with the defailt export format or something like a dropdown menu.