Create tool to look for gaps in SensorData

[cammoore]

Reported by rbrewer, Jan 10, 2012
It is currently straightforward to find out the first and last SensorData available for a Source using the source summary API call. However, this is a very crude measure of data availability, since there could be days or weeks with no data.

It would be useful to have a client that scans a source (or optionally all sources), looking for "gaps" where no SensorData is present. All gaps should be reported, and the gap size should be configurable. Note that SensorData can be stored at a variety of rates, which can vary over a long time period.

[rbrewer]

Related to #25

[cammoore]

May be a part of the 'machine learning' package