A little more configuration screen work

Laid out UI for part program editing form.
Made PartProgram properties read/write.
Implemented "add part program"

Initial part program add form working. Not saved to filesystem.
No way of removing thumbnail or setup file.
No way of editing existing part programs yet.
Implemented part program add/remove.

Implemented add/remove part program.
No mechanism for editing.
All changes saved to file automatically.