Draft: Clonable Pile-up Tools
A number of pile-up tools (in InnerDetector and MuonSpectrometer) weren't clonable because they contained ReadHandleKeys that were reset on initialization, which broke when there were multiple instances of the tool.
This MR turns those properties into StringProperties and initializes the ReadHandleKey from the StringProperty if necessary. The ReadHandleKey is still exposed as a (renamed) property but does not need to be set in any configuration.