Tidied up some styling options and improved comments

Trying to unify styling options into a "style" block to differentiate
them from other options and keep them self contained
Readded the labels to line charts
Added labels to destacked charts
Added background colours and borders to charts
Added the missing right hand bar on the grid
Added background colours to the chart bits of line / bar charts
Unified and reworked how keys are rendered

Unified the way that keys are rendered to make their widths more
dependant upon their actual content and to have them render in a
more uniform manner.

Also fixed some issues with graph scales on multiple line charts
which are not stacked
Added a new chart "AxisLine" which is a line chart with weird axis

The axis for an AxisLine are rendered at the sides of the chart
with a key to help show what is what
Fixed xaxis charts showing too many labels