standard layer name support from BOARD::GetLayerName().  This function evolved
in a contorted direction over time, and was being asked to return one of 3
different kinds of layer names, even though it only took a boolean to control
that choice.  

Users are better served by forcing them to get to know the concise new 
English Standard layer names.  This is because these concise names show up
in the "pretty" footprint/module files as the standard representation of
both feature and copper layers.

Change the name of BOARD::GetDefaultLayerName() to GetStandardLayerName().
Drop boolean argument to both BOARD::GetStandardLayerName() and 
BOARD::GetLayerName().