Recursively loading concepts shouldn't try to reload the concept more than once

When importing a concept into a dictionary, we use the function recursivelyFetchToConcepts() to load all of the concepts and then the mapped concepts for those concepts, etc. However, if a mapped concept is mentioned more than once, we can end up trying to load the same concept into the same dictionary multiple times. What we need to do is track the concepts being fetched an sure that each concept is only loaded a single time.