Simplify publish date checks

Fixes #814

- Changed to compare instances of `moment` using it's built in
comparison function instead of string compare with the date from the
database.
- Ensure compared date is parsed with the correct formats that we were
supporting before #1107.
- Moved date formats to variables to reduce chance for error in future.
Merge pull request #1122 from gotdibbs/Issue814

Simplify publish date checks