Create theme classes

Creates a light theme, using existing properties from the axis, series
and chart, and an abstract theme class.

Currently, the Theme only holds the structure of the theme without any
of the actual values. The LightTheme sets each of these.
Apply the theme from the ChartGroup downwards

Applies the theme to the chart group, and on to the chart, table, axes,
series, and gridlines.

Adds tests that new values are properly propagated.

Also fixed an issue with "gridLines" vs "gridlines", and an extra "-" in
@param comments.