Adding support for Chartjs 3

[weaverryan]

Q	A
Bug fix?	no
New feature?	yes
Tickets	Fixes #86
License	MIT

This takes the work from #126 and rebases so we can finish on the 2.x branch.

[tgalopin]

There seems to be a missing browser feature required by Chartjs 3 (ResizeObserver), perhaps would it be necessary to add a new polyfill.

[weaverryan]

There seems to be a missing browser feature required by Chartjs 3 (ResizeObserver), perhaps would it be necessary to add a new polyfill.

You're right - it WAS missing in the test environment. I polyfilled it there. But I don't think we need to polyfill it for the users, if that's what you meant (let me know if that IS what you were thinking and let's chat).

I have just one more tweak on this one - it's in the "externals" of the built file (if you build the file right now, the dist file will "contain" chartjs instead of just having the import line). I know the fix - I just need to make a nice addition to the build system for it.

[weaverryan]

This is now ready!

[tgalopin]

Could you squash your commits? I can't do it automatically due to two authors :)

[Huluti]

ChartJS is now at v3.6.2. Is it something to change in this PR since it's based on v3.4.1?

[weaverryan]

The 3.4.1 only means that it's the minimum version. In reality, if you installed this, you would have ^3.4.1 in your package.json, but yarn/npm would install the latest version 3 (so 3.6.2). It's really not a big deal one way or another, but I'd say just keep it.

I've got it rebased to only 2 commits - that's how (I think) we should keep it.

[tgalopin]

Thanks @weaverryan.