Add minimal GC card reader model.

Intended to be used with stripped wires as contacts.
Should be 3D-printable without any support nor raft. Beware of thin walls
which may be discarded by the slicer, causing overhangs.
Assembly notes:
- beware of shorts when using multi-fibre wires
- Kapton tape strongly advised to avoid the wires shorting against the
  card's shield
- not all contacts are necessary to read/write a card, refer to a pinout
  to know which places to populate
- contacts will likely not be perfect, be careful when inserting in the
  card. Some squeezing of the card may help.

Author: vpelletier