Improve python tracing of Import operations
Add event processing to pqSMTKBehavior, and call in the trace, so that the pipeline source is available when ParaView adds a call to GetActiveSource(). This pairs with an app change that blocks tracing the standard ParaView reader in favor of an SMTK operation.
Fix a bug in replay that crashed when the resource list was empty.
Fix a bug tracing operations with extensible items with one value.