GPS synchronization with autodrift improvements

With the GPS mod, the clock time will be synchronized to the GPS time
within a second.  The GPS corrections are again used to calibrate the
automatic drift correction.
Optionally flash dots-separators in time formats

The time display styles with dot-separators may be configured through
the menus to blink slowly, blink quickly, or not blink.  The previous
behavior was for all dot separators to not blink.