[4096] Added copy constructors and equality tools to client class storage

[4096] Added copy constructors and equality tools to client class storage

In anticipation adding client class storage to SrvConfig:

src/lib/dhcpsrv/client_class_def.h
src/lib/dhcpsrv/client_class_def.cc
    added copy contructor, equals() method, ==, != operators
    To ClientClassDef and ClientClassDictionary

src/lib/dhcpsrv/tests/client_class_def_unittest.cc
    Added copyAndEquality tests for ClientClassDef and
    ClientClassDictionary