Organizing the parts library

[Max Murtazin]

We are talking parts not model (ldr/mpd) files, therefore a strict "no". 

The part specifications don't allow a similar handling within the part (dat) files

Would be pretty neat if it did though. Most subfiles are essentially just a way to reduce file size and never reused outside the part they were made for. The spacing would be even more optimized if there was no need for precise names and separate files for data that's used for only a single part