1) when loading (default) preset, node name can be changed, so the
   reference to the node instance is no longer valid. So when loading a
   peset, we now return the instance of newly created node.
2) When saving a preset from Shift-P menu, is_node_preset flag was not
   set, so the preset was saved in incorrect format and could not be
   loaded as a node preset.
3) Use default presets when creating temporal viewers.