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 don't think we want to start the timers in `__init__`, but rather in `on_initialize`. There is no guarantee a context exists until `on_initialize` has been called, so it's probably better to have the Timer starting in there. We can save that for a future PR, though.