Saves having to serialize the note fields and q/a templates, which
is particularly a win when rendering question/answer in the browse
screen.
Also some work towards being able to preview notes without having to
commit them to the database.
- notes with wrong field count are now recovered instead of
being deleted
- notes with missing note types are now recovered
- notes with missing cards are now recovered
- recover_missing_deck() still needs implementing
- checks required
Some third party clients that create apkg files appear to be saving
a millisecond timestamp into this column. While this could also be
solved by increasing this field to a 64 bit number, some older clients
expect this column to be a 32 bit number.
