Add QA/QC features

[inkenbrandt]

Incorporate some programmatic checks into the program that allow for qa/qc of the final data, prior to it being entered into the database.

• significant change in rolling variance in the time series - we have been having a lot of issues with null units in many of our transducer downloads; if the processing misinterprets these units, it can cause a huge difference in the observable variance of the time series.
• water level above the casing top elevation - keep in mind that at a few locations, this is possible (ex. transducer in a piezometer that can become completely submerged in a pool)
• a check for negative, null, or unrealistic water elevation values
• I found that temperature can be used to eliminate spikes caused by freezing conditions or situations where the instrument is out of water
• a way to easily identify gaps in the record.
• check in correlation between output columns