fix: BarNote getSVGElement always returning undefined

[judocode]

BarNote is not opening its own context group which means it fails to perform operations requiring the id of the Element such as getSVGElement, addClass, removeClass etc.

I also added barline as a property of barnote to memoize it and have direct access to the barline if one needs it.

It looks like there are not any tests for the barnote directly but I added a test for the error scenario I was running into where getSVGElement was always returning undefined for rendered BarNotes

[AaronDavidNewman]

Hi @judocode I just pulled the latest version of your branch, did npm install and grunt webpack:debug. I see the following error in Barline tests.

I'm thinking your check should skip the undefined check if the renderer is canvas.

[judocode]

Ahh thanks @AaronDavidNewman - my tests were timing out for an unrelated issue it seems, but I added that check and was able to run all tests 👍

[AaronDavidNewman]

This looks good, thanks for your contribution.