Updated the "votes_per_day" method in graph controller to work better and

Updated the "votes_per_day" method in graph controller to work better and
read easier. Also, with Mako's insistence and help, wrote the "votes_per_interval" method (and helpers) in graph controller. The worst part of that
method is when I assign names to the labels_hash, ideas welcome, but it
works for now. Even though the graph uses fixed intervals and is named
"votes_per_interval" it actually shows votes over time (per interval),
so I may rename it in the near future (in fact I would've renamed it for
this commit, but I didn't think till I was writing this statement.)