Automatic iso surface determination

[jmmshn]

Automatically determine isosurface level

Current way that isosurface is determined needs to be updated.

• Added error reporting for invalid isosurface values
• Added a percentile based method if value is not provided
• Give more normalization options for the data
• Changed the call signature of the helper function slightly
• Added an example app

[mkhorton]

Thanks for adding!