Make at least the serial number configurable at some level

[Jakuje]

Using multiple smart cards results in the same tokens that look the same:

Slot 0 (0x0): Virtual PCD 00 00
  token label        : CAC II
  token manufacturer : Common Access Card
  token model        : PKCS#15 emulated
  token flags        : login required, rng, token initialized, PIN initialized
  hardware version   : 0.0
  firmware version   : 0.0
  serial num         : 000058bd002c19b5
  pin min/max        : 4/8
  uri                : pkcs11:model=PKCS%2315%20emulated;manufacturer=Common%20Access%20Card;serial=000058bd002c19b5;token=CAC%20II
Slot 1 (0x4): Virtual PCD 00 01
  token label        : CAC II
  token manufacturer : Common Access Card
  token model        : PKCS#15 emulated
  token flags        : login required, rng, token initialized, PIN initialized
  hardware version   : 0.0
  firmware version   : 0.0
  serial num         : 000058bd002c19b5
  pin min/max        : 4/8
  uri                : pkcs11:model=PKCS%2315%20emulated;manufacturer=Common%20Access%20Card;serial=000058bd002c19b5;token=CAC%20II

It would be good to be able to distinguish them with some configuration at some point.

This needs to be figured out if this can be done here or it will need changes in libcacard though