#349 Fixed concept graph mostly; I still need to get the mappings view rendering mapped nodes. I changed the cache REST call registry system to track serviced callbacks. Without this, callbacks get triggered whenever the view isn't or cannot be responsible with what they call for. If I were to reject calls rather than providing callbacks with cached data, then different callbacks using the same data would get caught. The combination of caching and callback service records makes for very efficient loading as well as effecient switching between concept graph types. It is all hidden from the view, except for the need to clear service records on a view switch without a page reload. Any messiness in the registry system is therefore not in the view.