[MergeDuplicates] Disable movement of other cards when dragging a sense card

"1. HH [Merge] When adding a sense from one entry to a different entry, make the existing senses stay still. (If they are still, then we will be able to merge one sense with another more easily.) Use some other visual indication of whether the sense I’m dragging will go into a sense, or between two senses (e.g., a line showing between the senses, to show where it will go). Right now it is really hard to manipulate these cards, even for experienced users, never mind those who have only just learned to use a mouse. There must be a better way."

This is not supported by the drag'n'drop package we use, react-beautiful-dnd. We may need to refactor on react-dnd.

Locate the drag-and-drop implementation using react-beautiful-dnd, then investigate whether react-dnd supports keeping existing sense cards stationary and showing the insertion position. Done means dragging a sense clearly distinguishes dropping into another sense from placing it between senses.