… scales

- Remove `chart.isCombo`
- Remove the includeOffset argument from `getPixelForValue()` and `getPixelForTick()`
- Add a new `offset` option to scales to add extra space at edges
- Bar controller automatically calculates the bar width to avoid overlaps
- When `offsetGridLines` is true, grid lines move to the left by one half of the tick interval, and labels don't move
- Add tests to the scales and the bar controller