Connections selected in a group move without endpoints moving

[bgribble]

This happens sort of erratically but it's surprising and wrong when it does.

Basically if there are multiple items selected, including connections but not their endpoints, dragging the selection drags the drawn connection but not the endpoint. I would say that connections should be exempt from dragging except to follow their selected endpoints.

[bgribble]

The commit above fixes this issue. If a connection is selected along with other items, and the items are dragged, the connection stays selected but doesn't move.