Adds axis containers and chart background

(Also fixes code style issues identified by @jleft https://github.com/ScottLogic/d3-financial-components/pull/104#issuecomment-65436328)

This change makes it easier to create a chart and add axes. Here's an example:

```
// Create the chartLayout (width and height not 
![capture](https://cloud.githubusercontent.com/assets/1098110/5296824/61f45b4c-7ba0-11e4-9d78-01a1b83a4dfe.PNG)
set)
var chartLayout = fc.utilities.chartLayout();

// Setup the chart
var setupArea = d3.select('#financial-chart')
    .call(chartLayout);

// create scales
var x = d3.scale.linear()
  .domain([0, 100])
  .range([chartLayout.innerWidth(), 0]);

var y = d3.scale.linear()
  .domain([0, 100])
  .range([chartLayout.innerHeight(), 0]);

// add axes
var bottomAxis = d3.svg.axis()
    .scale(x)
    .orient('bottom')
    .ticks(5);
chartLayout.getAxisContainer(setupArea, 'bottom').call(bottomAxis);

var topAxis = d3.svg.axis()
    .scale(x)
    .orient('top')
    .ticks(5);
chartLayout.getAxisContainer(setupArea, 'top').call(topAxis);

var leftAxis = d3.svg.axis()
    .scale(y)
    .orient('left')
    .ticks(5);
chartLayout.getAxisContainer(setupArea, 'left').call(leftAxis);

var rightAxis = d3.svg.axis()
    .scale(y)
    .orient('right')
    .ticks(5);
chartLayout.getAxisContainer(setupArea, 'right').call(rightAxis);
```

Which produces the following:

![capture](https://cloud.githubusercontent.com/assets/1098110/5296828/6cc119f2-7ba0-11e4-993e-1e7d33ba71a2.PNG)


This background element is appended after the clipping path, which the series etc. are added too, so this background element will be drawn over everything in the plot area.

I think this should be added as the first element in the chartArea group, so it remains in the background.

There are a couple of ways to do this:

- [append](https://github.com/mbostock/d3/wiki/Selections#append) the `rect` after creating the chartArea group and before the clipping path (around line 53)
- Use D3's [insert](https://github.com/mbostock/d3/wiki/Selections#insert) method and specify that it should be inserted as the first child of the chartArea group:
```
chart.insert('rect', ':first-child')
    .attr('class', 'background')
    .attr('width', chartLayout.innerWidth())
    .attr('height', chartLayout.innerHeight());
```