Change default Matrix transform order to Prepend

Add specific RotateAppend, TranslateAppend, etc routines, instead of specific Prepend options. Fix up Samples and Tests accordingly, and add extra MatrixTests and TransformTests to differentiate Append and Prepend orders.

It is more consistent to make Prepend the default Matrix order, with Append being available as an option.  This is particularly relevant now that Context.ModifyCTM allows Matrix transforms to be applied to a Drawing Context.
This means that multiple Matrix transforms are now done in the same order as multiple Context transforms.