Keep trip shape after stop has been edited

[maxwell8888]

Currently, for trips that have an associated shape, if a stop within that trip is changed, we disregard the entire shape and simply interpolate between each individual stop. An improvement would be to use the shape between each stop which has not been edited and only interpolate between stops where one has been edited.
There are problems with this however.
What if the user wants to continue to use the existing shape because the new stop added is on this shape?
What to do if the user wants to save the file not having updated the shape? Just have that one particular shape missing? Use the old one? Automatically create a new one interpolating between the stops?