Raw (digitized) hit model redundant, use single unified RawHit

Currently all digitized hit structures store the same basic information: 64bit cell ID, 32bit time stamp and 32bit value. There is no good reason for them to be separate classes. We should unify them into a single RawHit structure as this will provide us with more flexibility down the road. And when needed we can add data structures that actually store different information as we go. Proposed structure:

RawHit:
  Description: Raw detector hit storing one 32-bit word of information 
  Members:
     - uint64_t         cellID
     - uint32_t         timeStamp
     - uint32_t         value