Initial sketch of bug #282, aggregate cell data export.
Address review comments on cell data export code, cc #282.
Fix minor typos/bugs preventing S3 upload from working.
Adjust export format to conform to agreement with OpenCellID
Add import/export doc.
Add once-a-day full export.
Normalize psc=-1 to empty field on export.
Use reduced redundancy and inherit ACL on export.
Rewrite export code to avoid ORM.
Document averageSignal as dBm, not ASU.
Fix definition of CDMA BID in export docs.
Fix daily full-export task to actually be daily, be called 'daily'.
Fix hourly export to snap time window to enclosing hour, exactly.
Reorder imports a bit
Small doc improvements, wrap long lines.
Use fewer cells in tests to speed up test runtime.
Remove year/month from export key name.

We'll only have a limited number of files available, so there's no
need to use nested folders.
Move the export cell task to be run shortly after midnight.

And move the backup tasks back a bit.
Use a hourly boolean flag to distinguish between daily/hourly export job.

Also remove the modified condition from daily queries. And make the export
filenames a bit more predictable by setting minute/day to zero for hourly
jobs and additionally daily to zero for daily jobs.
Remove unused now argument, but move up columns definition to calling functions.