Expanded documentation of mouse (and keyboard) events

[psobolewskiPhD]

🧰 Task

There is existing documentation of event handling, but it's fairly thin and a bit scattered.
Meanwhile, reacting to mouse (or keyboard) events is a very powerful napari feature, and something that an intermediate napari user should be able to access in a clear fashion.
For example, it's not clear or intuitive how to react to a single click. Once it's documented, it may end up that we need a convenience function in napari/napari.

Dedicated issue for keyboard events: #413

• Mouse events docs refer to a MouseProvider which doesn't appear to exist:
  https://napari.org/dev/howtos/extending/connecting_events.html#listening-for-mouse-events

[imagesc-bot]

This issue has been mentioned on Image.sc Forum. There might be relevant details there:

https://forum.image.sc/t/napari-unable-to-pan-in-perspective-mode/101796/2