Added Offset, Top and Height YAxis options.

http://api.highcharts.com/highstock#yAxis.offset
http://api.highcharts.com/highstock#yAxis.top
http://api.highcharts.com/highstock#yAxis.height
Style fixes.

Replaced tabs with spaces, removed trailing spaces, etc.
Removed Offset.

It was already part of the XAxis class so it wasn't needed in the children.
Expanded the demo to use the new options in YAxis.
Added the Highstock compare demo.