Uncouple series and chart

Pulls out the chart argument from a series constructor, and makes sure
the series has no back-references to its parent chart.
Renames chart.chart => chart.plotArea

This had been confusing me a lot, as I thought chart.chart was the same
as chart. Turns out its the HTML node for the corresponding chart, where
we add all our lines, points, etc. It makes more sense to differentiate
it by calling it a plot area.
Pull out tooltip

Moves all the tooltip creation code into the series itself, and has it
execute on a draw().
Removes "chart" from Axis constructor

- Uncouples the chart from the axis by removing it from the constructor,
  instead using the chart.addAxis() method.
- Moves the barPadding method from the chart to the axis
- chart.bounds now set by calculateAxisBounds, where width=[0], height=[1]
Split axes into x and y axes

Splits apart the axes property of the chart into xAxes and yAxes.
This removes the require for a "direction" in the axis constructor,
setting it when the axis is added to the chart.
Remove anchor from Axis constructor

Removes the top/left/bottom/right argument from the axis, replacing it
with the reversed() method. The anchor/orientation is now derived from
the reversed() and horizontal() methods.

The anchor and orientation values appeared to be representing the same
thing, so we now just use the orientation() instead.
Fix zooming for date axes

The axis needed to have had the domain initialised in the axis draw,
before the zoom is initialised.
Merge branch 'upstream' into feature/refactor-initialisers

Conflicts:
	insight.js.zip
	src/charts/Axis/Axis.js
	src/charts/Chart.js
	src/charts/Series/LineSeries.js
	src/charts/Series/RowSeries.js
	src/charts/Series/Series.js
	tests/Axis.spec.js
Merge branch 'feature/refactor-initialisers'
Address comments from code review

- Updates calculateAxisBounds comments
- Removes drawGridLines from Axis (it is now on AxisGridlines)
- Updates drawGridLines comment in AxisGridlines
Merge pull request #78 from tpkelly/master

Refactor initialisers