store copies of model objects in the selectedObject property
differential editing no longer happens in-place
whoops, should be using instancetype
selected terms are no longer edited in place
changes how terms are searched through under a click, since we can no longer compare identically
changes the model-to-modelview maps to be keyed on EXTLocations, to deal with non-literal equality between the model objects and the selectedObject object. this fixes differential highlighting, but it hasn't fixed term highlighting.
add -updateChangeCount: messages to multiplicative annotation edits. this is a little lazy, since this should probably be in EXTDocument alongside the other similar routines, but things are laid out a little differently for multiplicative annotations so i've instead decided to cluster all of their stuff together in one place