Factor out the FP_LIB_TABLE specific content from FP_TBL_MODEL into a new
LIB_TABLE_GRID class that can be used for any library table grid mix in.
Create new FP_LIB_TABLE_GRID object for the footprint library edit dialog.
Add method GetEnvVariables() to return any environment variables found in
a LIB_TABLE object.
Wayne Stambaugh