monitor.go: signal timestamp from UTC to local time

[Russell Stanley]

Currently, the time of the latest signal on the vidgrind monitor page is viewed in UTC. This should be converted to the local time for the current user.

[Trek Hopton]

Note: each site should have a timezone associated with it. See iotsvc/iotds/site.go ln:46.

[David Sutton]

Addressed in pull request #207