Add Lincomatic Teensyduino defs as a AT90USBxx_TEENSYPP_ASSIGNMENTS option 

This should enable less conflicting pin assignments for the AT90USBxxx chips by enabling a AT90USBxx_TEENSYPP_ASSIGNMENTS option.  Default behavior if  undefined should use the old pin definitions and not upset existing configuration files.

This should close https://github.com/ErikZalm/Marlin/issues/703 and https://github.com/ErikZalm/Marlin/issues/112