Axis default positions

[etimberg]

This PR contains 2 changes.

1. Removed the references to Chart.Controller from the JSDoc comments
2. When creating axes, we now define the default position for axes. If the position option of the axis does not match the actual location, we change the position. This prevents incorrectly formed charts and has been heavily requested.

Example:

let options = {
  scales: {
    xAxes: [{
      type: 'linear',
      position: 'right' // will be changed to 'bottom' since 'right' is not an x axis
    }],
    yScales: [{
      position: 'bottom' // will be changed to 'left' since 'bottom' is not a y axis position
    }]
  }
};

[simonbrunel]

Looks good, is unit tests pertinent for this change?

[simonbrunel]

[minor] can we keep the condition on the same line, quite confusing when reading :) ?

[etimberg]

Sure, I will make that change

[etimberg]

I added a unit test to cover this.

[simonbrunel]

+1 to merge! what's the reason unit tests values required adjustments?

[etimberg]

Previously, there were 3 axes in the chart in that test (1 on the x, 1 on the y at position 'left' and one on the y at position 'bottom' so I cleaned it up to have only 2 and mimic the old fitting but the sizes changed slightly

[skhan02]

@etimberg any idea on how i can get the axis labels to render with the x-axis instead of top or bottom?