'Returns the label for the X-axis tick index,
and a boolean indicating whether or not it is aria-hidden'

def x_tick_label(self, tick_index):

    selector = self.q(css='#grade-detail-graph    .xAxis    .tickLabel')[tick_index]
    tick_label = selector.find_elements_by_tag_name('span')[0]
    return [tick_label.text, tick_label.get_attribute('aria-hidden')]
