Several fixes to entity implementation

[sebastianburckhardt]

Three fixes in this PR for issues that were discovered during testing:

• some of the design changes for OperationResult were not fully reflected (was still using errorContext/ ErrorMessage)
• did not have enough parameter checking for entity ids that are passed in
• the orchestration executor was not being passed the entity backend parameters

Also, one design changes per online discussion

• add a TaskEntityOperation parameter to the InitializeState call