title: chart.js Line chart with different background colors for each section
body: <p>Lets say I have a Line chart with mon-fri for 4 weeks.
  I want that these 4 weeks are diveded in sections. I want the first monday to friday have a white background color.
  The second monday to friday a gray background.
  The thirth a white bg again.
  And the fourth weeks with monday to friday to have a gray background color.
  What Im talking about is the background of the graph.
  Is there a way to do this?</p>