Issues in Events.2017 file

[andybega]

There are several issues in the "Events.2017.20201006.tab" file. I'm gonna use this issue to document them in one place.

• 1. the dates are in a non-standard "" format (see #57, fixed in cb75754 by special treatment in read_events_tsv())
• 2. there is no "CAMEO Code" column (#74)
• 3. some text fields are quoted in the raw tab delimited data files (#75)

This is also going to require instructions on how to fix events already in the database, for those using it:

• 4. instructions on how to fix database