Connection.loadFromURL was swallowing all the errors instead of passing them along
WIP: added iD.Graph#expire to remove already deleted nodes from base
(probably not going to keep this though)
Add entity copy methods
Added iD.actions.CopyEntity
Handle merges where a locally *modified* entity has been deleted remotely.

If the entity was modified locally, we can safely put it back.
1. make a copy of the entity
2. delete the original.
3. add child nodes/ways to the toCheck queue (because maybe they were deleted too)

The new copy will be put into the changeset as a create with placeholder id.
The delete will be sent to the server (but ignored as of openstreetmap/openstreetmap-website/#858)

Related: #2475