Use time.process_time() instead of deprecated clock()
This fixes:
DeprecationWarning: time.clock has been deprecated in Python 3.3 and
will be removed from Python 3.8: use time.perf_counter or
time.process_time instead
[web] Make the time separator configurable in JQueryDateTimePicker
We add a "separator" argument to JQueryDateTimePicker which will be used
when creating the underlying JQueryTimePicker instance so that the user
can control how time is displayed by the widget. This is very similar to
the "timesteps" argument that's already present.