Gear hub interface update

According to the specifications on Pivotal, the global variable
"gearhubintwid" is now 12.21mm instead of 15mm (1/2 red gear width
thinner) and the set screw hole is made. The updated file is now called
"GearHubInterface_Tilt_v4_2. I will print tomorrow.
Updated Shaft Collar, Tower Front

1) Created a tower front without pegs that go into the pan surface to
better support the axle holding the marker (See
TowerFront_Left_v4_3_Pegless
2) Doubled the width of the shaft collar for horizontal stabilization
and changed the stress set screw size for brass screw insert (See
ShaftCollar_v4_Final). Equations are up to date for the current
dimensions
Creating full system CAD