Add buton to reset graph

[ioresult77]

I am really happy, that now all manipulations with graphs are reflected in main windows's URL and not just in the URL of the picture. Yet, before that feature was implemeted, I could easily reset graph by hitting F5 to reload browser window and now I have to make many clicks to achive the same result.

I suggest to add a button on the toolbar, which will remove all datapoints from the graph in one click.