Adding zoom in/out with scroll wheel functionality to `BlCanvassableElement`

[botwhytho]

With this we can easily levarage in classes like GtScenery, GtPresenterCanvas, etc. and simplify existing logic in GtPhlowMondrianView>>#asElementDo:

Below is a video of functionality we get for free in various scenarios that use the class. PRs incoming.

BlCanvassableElementZoomWithScrollWheel.mp4

[botwhytho]

PR Created feenkcom/bloc-pac#3

[botwhytho]

PR Created feenkcom/gtoolkit-visualizer#12. Removes logic that currently lives on GtPhlowMondrianView >> asElementDo: as it will now live in a more generic place in BlCanvassableElement

[girba]

Thanks. We will look at it.

/cc @syrel

[botwhytho]

Zooming + Translating in same smooth motion after adding functionality.

BlCanvassableElementZoomWithScrollWheelAndTranslate.mp4