'Add a yaxis label to the current subplot in layout dictionary.
props.keys() -- [
\'text\',         (actual content string, not the text obj)
\'position\',     (an x, y pair, not an mpl Bbox)
\'coordinates\',  (\'data\', \'axes\', \'figure\', \'display\')
\'text_type\',    (\'title\', \'xlabel\', or \'ylabel\')
\'style\',        (style dict, see below)
\'mplobj\'        (actual mpl text object)
props[\'style\'].keys() -- [
\'alpha\',        (opacity of text)
\'fontsize\',     (size in points of text)
\'color\',        (hex color)
\'halign\',       (horizontal alignment, \'left\', \'center\', or \'right\')
\'valign\',       (vertical alignment, \'baseline\', \'center\', or \'top\')
\'rotation\',
\'zorder\',       (precedence of text when stacked with other objs)'

def draw_ylabel(self, **props):

    self.msg += '                                Adding    ylabel\n'
    axis_key = 'yaxis{0}'.format(self.axis_ct)
    self.plotly_fig['layout'][axis_key]['title'] = props['text']
    titlefont = go.Font(size=props['style']['fontsize'], color=props['style']['color'])
    self.plotly_fig['layout'][axis_key]['titlefont'] = titlefont
