Update the new classes in CondFormats for the CondDBv2 usage

This implies:
- Edit the header file for the new class in interfaces and add
    * the include statement for the serialization
    * COND_SERIALIZABLE; at the end of the Phase2TrackerCabling and Phase2TrackerModule classes
    * COND_TRANSIENT after the declaration of the transient members of Phase2TrackerCabling
- Add a non const method to perform the initialization
- Register it using REGISTER_PLUGIN_INIT macro in CondCore/SiStripPlugins/src/plugin.cc
- Edit CondFormats/SiStripObjects/test/testSerializationSiStripObjects.cpp and add a line for the new classes

I also took the opportunity to add the CondCore/SiStripPlugins/plugins/Phase2TrackerCablingPyWrapper.cc