Bug 986701: Script for cleaning FxOS 'ftu' pings.
Add MPL blurb
Support for source-bucket == dest-bucket
Add required __init__ files.
Don't try to remove nonexistent files.
Add a "min-date" parameter to skip old files.

We will use this to avoid reprocessing the entire history when
source-bucket and dest-bucket are the same.
Merge pull request #66 from mozilla/sanitize_fxos_bug986701

Sanitize FxOS pingIDs bug986701