Adding ability to make user clock adjustments

Sometimes there might be significant differences between a user's clock
and that of the server, and you want to use the server clock instead of
the user's clock.

This change adds a KairosTimeFrame.setClockAdjustment function
and centralizes logic that calculates "now" into a single
KairosTimeFrame.clock function that uses the clock adjustment value to
"adjust" the value of "now"