Add subscription option and depth support for collection nodes.
- Add get_parent_nodes/2 and get_parent_nodes_tree/2 to
gen_pubsub_nodetree behavior. These functions act like their
subnodes counterparts, except get_parent_nodes_tree, which also
includes the depth of the node from the root of the selection. It
might be a good idea for get_subnodes_tree/2 to do the same thing,
but isn't required.
- node plugin's get_node_subscriptions takes a list of nodes, not a
single one now. This is to better split the concerns of nodetrees
and nodes. It's still not perfect, as the case of a nodetree which
has nodes of different types isn't handled.
- Catch errors when trying to delete nodes which don't exist.