Histogram does not place commits in the correct day

[rmyers]

The current histogram is not very smart. It just creates a list from the days returned, this means that if there are no commits on day 3 but there are on day 4 they appear on day 3. We need to inspect the data coming back and fill in zeros for the missing days. Also we should change the front end to accept a json object like:

{'count': 9, 'label': '2013-07-04'}