Zoom in and out of canvas

[thisisaaronland]

There were some early tests using escobar5/raphael-pan-zoom which:

• Works in a desktop context but, as written, don't update the position and offset of the raphael-sketchpad pen so paths don't appear where they should.
• Seems to work correctly in a mobile context except that the entire HTML canvas, rather than just the SVG element, is zoomed in and out.

[straup]

https://dmitrybaranovskiy.github.io/raphael/reference.html#Paper.setViewBox

There are two things to figure out:

1. UI/UX for taking raphael.sketchpad out of editing mode and listening for pan/zoom events
2. Adjusting the offset (_offset) for the pen in raphael.sketchpad