reorganize DataHandleHolder visitor acces to avoid non-retrieved tools

This is not a perfect fix, more a workaround.

The method initToolHandles have been modified to fill the list of used ToolHandles only with the tools retrieved explicitly in the initialize method.

GaudiCommon required the introduction of a hook so that the custom fixer visitor could be created in the GaudiCommon::initialize, but used only at the end of PBASE::sysInitialize (eb392741).

I also fixed an issue (double delete) with the use of ToolHandle from GaudiCommon (0a1bec8).

Fixes GAUDI-1183.