[Bug 867122] Deal with lack of data in kb history.

Two things happened here:

* The view was not extending data to the present day. On most archived articles, that means that the default viewing window for k.Graph shows no data, which makes it angry. This commit makes the view add zeroes to the data to fill it in.
* k.Graph couldn't deal with series of all zeroes, or other strange data sets. This commit added some checks for good graph scales.
* Series used to calculate minimums as well as maximums. This wasn't used, so I axed it.