Open-CloseD sign

Still W-I-P. Sharing because comments on the original asked for some of these improvements, and because several things changed from Quintox303's design:

1. Added the D
2. Pins/holes to locate the letters accurately.
3. Two-part base for printing on smaller beds
4. Improved E- and S-gear axles

Updated but not yet printed by me (7 Feb):

1. Improve the E- and S-gear axles more... they're still weak.
2. Chamfer bottom of D, E and S and top of C, L, and R main gear

Still to do:
3. Thicken E- S- and sun-gears
4. Add small bearing surfaces to base to lift gears off base for reduced friction
5. Move main axles slightly (3-4mm?) closer together to reduce play
6. Stops to stop rotation when in correct alignment.
7. Increase base size behind the D
8. Increase height of main axles