Incorrect use of local timezone

[maxg]

Plug-in:

• sharedb.js#33 - published checkoffs not shown to users who are a day ahead

Web:

• dashboard/checkoff.js#13 & #70, dashboard/pings.js#119 & #127 - checkoff modification time incorrect
• dashboard/collabs.js#5 - collaborations incorrectly omitted or included by query
• collab.js#28-29 - potential incorrect earlier/later times around clock change times