- changing the digit format to now come as a linked list instead of an array

- changing the digit format to now come as a linked list instead of an array
  - will slow down digit maker, but give a significant speed up of the clusterizer at high multiplicities
  - also need to always ship the full list of digits, even after clusterisation, but
    this is anyway needed if one is to provide AliESDCaloCells in the ESDs
- now sorting the digits