init checkin of code to record which CellMeasures we can safely
archive into S3
* added `archive_batch_size` option to ichnaea configuration
* added a CellMeasureBlock model and alembic schema migration to track
  blocks of CellMeasure records to be archived
* added a `schedule_measure_archival` taks to compute blocks of
  CellMeasure records that we will push to S3
added tests to make sure that the CellMeasureBlock is actually
journalled correctly
initial test to make sure that CellMeasureBlock records are properly
journalled
Merge branch 'master' into features/188-tinydb
added basic testcases to make sure that the boto s3 calls are correct
changed s3 backup to a class to maintain keys for S3
added tests around uploading measurement archives up to S3 using a celerytask
added a SHA1 hash on file uploads to S3 so that we can verify uploads async with the backup process
added task to clean up CellMeasure records if the archive is valid
dropped CellMeasureCheckPoint
changed start_cell_measure_id and end_cell_measure_id to start_id  and
end_id
renamed methods so that i can tease out a wifimeasure version of the
cellmeasure backups
fixed a couple off by 1 errors when computing batches
flake8 fixes
dropped CellMeasureBlock in favor of MeasureBlock to consolidate
tracking of Cell vs Wifi measure archival
renamed CellMeasureBlock to MeasureBlock
refactored out Wifi backup code
added tests for delete tasks
changed the way that S3 connections are made to properly use the IAM data
updated test cases to reflect new API calls to use S3 via IAM
dropped WifiMeasureBlock (dead code)