Refactor ser/des code for dbcon/joblist and primitives/primproc

As of 6.1.1 serialization of similar objects that derives from Command class is broken into two parts:

• serialization in dbcon/joblist, e.g. ColumnCommandJL::createCommand()
• deser in primitives/primproc, e.g. ColumnCommand ctor.

This layout complicates ser/des changes so that this functionality must be separated into a translation unit stored in ./utils/serialization.