Let all dynamic examples run at 60 fps

This does a few things:

* Remove call to `canvas.update()` from `on_draw` in all examples. Use a timer instead.
* Gives `canvas.update()` an optional event arg (which is not used) so it can be used as an event handler, simplifying code that wants to call `update` via a timer.
* Improve measure_fps.

Todo:

* [x] If everyone agrees with the update of the `canvas.update()` method, use it in places where we now use awkward lambda. Otherwise change where I used it already.
* [x] Update use of timer to move `connect` and `start` in the initialize call.

Closes #229
I think that makes sense. Right now the default timer rate is zero. I hope no code relies on this. @lcampagn WDYT?