Trim old measurements past 10k, close #97, close #123
Add trailing comma.
Return 0 rather than None from get_curr_stat
Avoid persistent date objects in default arguments
Add indexes for {Wifi,Cell}.total_measures
Refactor trim functions to use 5-tuple identity for Cell/CellMeasure
Merge pull request #122 from graydon/bug-97-limit-number-of-records-per-wifi

Add task to trim excessive measurements, keeping most recent 10k, closes #97