Implement throttle and debouncing

[ianhi]

Problem

It is nice to sometimes be able to the throttle or debounce the updates to plots. See discussion in jupyter-widgets/ipywidgets#663 for an example for using with matplotlib.

Proposed Solution

1. Provide a method for setting ipywidgets sliders to continuous_update=False
2. Take the throttle and debounce examples fromm https://ipywidgets.readthedocs.io/en/latest/examples/Widget%20Events.html#Debouncing

For the throttling and debouncing I'm not exactly sure of the api. I think the simplest implementation (adding the fewest kwargs) is to apply them via the controls object and have them apply to all sliders.

controls.debounce(True/False)
controls.throttle(True/False)

or perhaps allow specifying only certain parameters

controls.throttle(True/False, 'tau')
controls.throttle(True/False, ['tau', 'beta'])

but that second version is more of a hassle.