Add a check of object type to `add_edges` and `add_nodes`

[ianhi]

Checks should be added to add_edges and add_nodes that the node/edge being added is actually a valid node/edge object and if not we should fail with a clear error message.

Originally posted by @ianhi in https://github.com/QuantStack/ipycytoscape/issues/214#issuecomment-748176164

cc @sven5s