Create ETL to check for missing crashes with missing CR3 pdfs

[johnclary]

We should set up a daily check to make sure that all crashes have a CR3 PDF downloaded. We cannot enforce this check in our CRIS import ETL, because CRIS only includes PDFs for new crashes.

To check for crashes without a PDF, we must exclude pre-2014 crashes and temp records. E.g.

select id, cris_crash_id, crash_timestamp from crashes
  where cr3_stored_fl is false and is_temp_record = false and crash_timestamp > '2014-01-02';

See also these related PRs:

• CRIS import ETL: check if crash report directory exists  vision-zero#1544
• Handle smaller cr3 pdf page size vision-zero#1529
• Better error handling when there are no crashes to process vision-zero#1518