Potential axes work

[novemberborn]

The createAxesMixin is far from complete:

• It assumes datum values are >= 0 for horizontal axes (no negative values), but <= is supported for vertical axes
• Axes configuration cannot be provided through the widget state. This would also require label selectors to be defined on the prototype since they can't be serialized into the state. Perhaps as topInputLabelSelector, etc
• Axes configuration cannot be provided through the prototype. This is necessary to create widgets with a default configuration
• It's unclear how a default configuration would be extended through options and/or state
• Certain configuration may be default for all enabled axes (e.g. ticks). Would be cool not to have to repeat that
• Chart dimensions are not adjusted if exceeded by grid lines
• No support for "mini ticks". These should probably be restricted to range based axes, where the step size must be a multiple of the mini tick interval
• Consider center (vertical) and middle (horizontal) axes for charts with negative values
• Our targeted IE versions may not support dominant-baseline. If we know the line-height we may be able to polyfill the currently limited set of allowed values, or maybe we need to support a perpendicularOffset option and remove dominantBaseline
• We may need perpendicularOffset anyhow (e.g. for the bottom axis it would move the label down, for the left axis it would move it further left)
• Axes tend to draw duplicate ticks and grid lines for the "zero" position