First published date fixes: time zone, database field type, and new doc date picker

[jacqui]

Closes #336 - fun with time zone conversions in javascript, hasura and postgres Closes #337 - now initializes the datetime picker in the sidebar for google docs that haven't been previewed or published yet

Test using latest code in the script editor:

• date is once again stored in postgres as timestamptz
• the sidebar code calls this function to format it (without converting time zone): https://stackoverflow.com/a/17415677
• date is then converted by postgres/hasura to UTC

You can also see that the datepicker is now appearing on newly created docs (not yet previewed/published in hasura) by testing with the latest code using the document "Brand New Article Testing Date Picker", which for me appears as the last test case in the editor's list.