Load/append a persisted test executive to an in-memory test executive

[Steve Ball]

1. Loading a persisted test executive can currently be accomplished by using a subroutine. This implementation requires a subsequent save and load to disk to then run correctly. This save/load could be removed to simplify the operation.
2. A preferred implementation would add a method to the API to load a xml from disk and append the steps to a provided parent ID, removing the need for a subroutine altogether.

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