Circular Printbed Calibration Pattern v2

This version adds customizer support. Note that you may have to rotate the customizer view a bunch of times for the pattern to display properly. (It looks like customizer does not like looking straight into a cut.)
Like the original version, some versions of Repetier Host require you to do a "fix normals" on the generated STL to allow the whole thing to print.
EDIT #1: Change the big number variable to not depend on layer height, in case someone chooses a miniscule layer height.
EDIT #2: Allow setting number of rings to 0