Changed scales to v3 version

[phiphphi]

I wanted to use stacking bar charts but saw they switched up how axes were handled, so I changed that and some other renaming fixes. This might be some help with the v3 migration - I fixed the tests but I'm not sure if this would break some current functionality, so it might merge into the development branch instead.

Changes:

• [x] scales.[x/y]Axes arrays were removed. Scales are now configured directly to options.scales object with the object key being the scale Id.
• [x] scales.[x/y]Axes.barPercentage was moved to dataset option barPercentage
• [x] scales.[x/y]Axes.barThickness was moved to dataset option barThickness
• [x] scales.[x/y]Axes.categoryPercentage was moved to dataset option categoryPercentage
• [x] scales.[x/y]Axes.maxBarThickness was moved to dataset option maxBarThickness
• [x] scales.[x/y]Axes.minBarLength was moved to dataset option minBarLength

Todo?

• [ ] More work on refactoring scales? Might add position field for custom scales Example of custom scale:

  options: {
  scales: {
    myScale: {
      type: 'logarithmic',
      position: 'right', // `axis` is determined by the position as `'y'`
    }
  }
  }

[mattosaurus]

Thanks for submitting this, I'll take a look over it in the next day or two.

I think quite a few of the other models have changed from v2 to v3 so I might try and update these at the same time.