Bug in min/max calculation of Histogram and Distribution plot.
Merge pull request #398 from jepebe/log_min_max_bug

Bug in min/max calculation of Histogram and Distribution plot.
ERT-514 Export of plot to png, clean up of code
Merge remote-tracking branch 'upstream/master' into ERT-514
ERT-514 Export of plot to png, moved file dialog in front of rendering so if the cancel button is pushed no image is rendered.
ERT-514 Export of plot to png, set rendering to be progressive
ERT-514 Export of plot to png, refactoring plot_metric_widget and plot_window