CLT-87 & CLT-88 Address core review comments

Changes:
- recovered some public APIs in the AbstractTdLogger for single key/value logging
  in log table and added the equivalent for item table
- made private member variables of the DbTableDescr and derived final
- reduced code duplication among the various version of the constructors for
  DbTableDescr and derived
- use @Override for our base to derived function member overrides and
  for interface definitions in function method implementations
- used standard definition for hashCode() and equals() as generated
  by Eclipse
- removed unused methods
- enclosed access to bufferPacker objects within existing synchronized blocks