Setting time from web interface for Raspberry Pi

Nalanda requested this feature.

Problem:
*Raspberry Pi has no internal clock battery.
*Records are incorrectly datestamped as a consequence.

Solution:
*Allow an administrator to change the date through the web interface, enabled for the Raspberry Pi only.

Tested on local machine, running as sudo.

More testing?

Check it works on a Pi without explicitly running as sudo - may need a sudo added to the os.system command if so.