plots should force output cells to be larger when `autosize` is `False`

[theengineear]

From http://stackoverflow.com/questions/30416871/plots-getting-getting-chopped-off-in-python-notebook

[jonmmease]

Setting the axis automargin property to True now takes care of the problem of axis ticks getting chopped off. If there are other components to this we can open a new issue.