Made various changes and additions to the device generator scripts

for magic for sky130:
1) Added internal spacing between the 3.3V nfet device and guard
   ring so that multiple cells can be abutted without causing an
   HVNTM spacing error.
2) Corrected missing vias over contacts for snake resistors
3) Added port labels to most of the device types (which should make
   LVS easier)
4) Added an option to the lower MiM cap to increase the internal
   spacings in a cap array so that it becomes compatible with the
   upper MiM cap spacing, so that MiM caps can be easily stacked.