Added accessor methods to chartLayout

The accessors means that we don't have to expose the structure
I've also added a class to the chartArea, having a 'g' selector felt a bit dangerous!
Added callback properties for components so that consumers don't need to conform to a particular data model.
Merge branch 'master' of https://github.com/ScottLogic/d3-financial-components
Merge pull request #104 from ColinEberhardt/master

Added accessor methods to chartLayout
Merge branch 'master' of https://github.com/ScottLogic/d3-financial-components

Conflicts:
	dist/d3-financial-components.js.map
	dist/d3-financial-components.min.js
	dist/d3-financial-components.min.js.map
	examples/_dependencies/js/d3-financial-components.js.map
	examples/_dependencies/js/d3-financial-components.min.js
	examples/_dependencies/js/d3-financial-components.min.js.map