Update user-status to keep track of status per host/channel.
rename digest to updates to better convey its meaning.

This prepares us for email digests!
Add setEmailDigestTime
Split off handlers/digest from handlers/updates.

* Add a new config item, sendEmail
* rename the email_digest_time column to last_digest_time
* rename thhe last_digest column to last_update_time
* rename db.js->setEmailDigestTime to setDigestTime
* handlers/updates.js calls user.getCurrentUpdates instead of getCurrentDigest
* To user.js, add getCurrentUpdates, setLastUpdateTime, getLastUpdateTime.
* To user.js, update getCurrentDigest to get digests instead of updates.
* To user.js, add getLastDigestTime, setLastDigestTime, and have sendCurrentDigest take an email (temporarily)
Rename the "sendEmails" config option to "send_email"