Increase plot margins by one week so that points are not cutoff

[ArtPoon]

Suggestion from @rneher

[ArtPoon]

Actually points representing observed counts are also cut off at the top:

but on mouseover the point is no longer clipped:

If we override this clipping for all points, it might make them easier to see - but it might also be a problem for large points (large sample size = large point area).