Merge branch 'GAUDI-1183' into 'master'

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 `ToolHandle`s 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.

See merge request !120