CAD: Move flap thickness slop to spool slop (scottbez1#114)

This increase was a mistake. The difference in thickness (0.2 on either side) should have been added to the *spool* slop instead of the flap width slop, as the inner width of the spool (flap_width_slop) was not affected by the thickness parameter, while the outer width of the spool (spool_width_slop) *was*. This commit corrects that oversight.

This reverts commit a68fc98 (squashed as part of 7be69db).

On my test display the spool will sometimes stall while rapiding. It appears that this is caused by imperfect assembly of the spool and the flaps sliding sideways, causing them to get caught on the upper corner of the front panel. I've traced the issue back to this change and I'm hopeful this PR will fix the issue.

Nudges this from 4 mil to 6 mil, just for that little extra clearance to avoid binding. (And for peace of mind)

3d/splitflap.scad

@@ -117,9 +117,9 @@ letter_color = color_invert(flap_color);  // inverse of the flap color, for cont
 flap_rendered_angle = 90;
 
 
-flap_width_slop = 0.5;  // amount of slop of the flap side to side between the 2 spools
+flap_width_slop = 0.15;  // amount of slop of the flap side to side between the 2 spools
 
-spool_width_slop = 1;  // amount of slop for the spool assembly side-to-side inside the enclosure
+spool_width_slop = 1.4;  // amount of slop for the spool assembly side-to-side inside the enclosure
 
 spool_tab_clearance = -0.02;  // for the tabs connecting the struts to the spool ends (interference fit)
 spool_retaining_clearance = 0.10;  // for the notches in the spool retaining wall