`psutil` does not contain these creation flags but supports
`subprocess`'s, so the one from `subprocess` needs to be used in order
for the process to be created properly.
If the project is not saved at all, it will suggest to save it manually
or to define a project in a temporary folder using date/time for the
project name.
Reoganization
- BaseNode: is the base class for all nodes
- Node: is now dedicated to python nodes, with the implentation directly
in the process function
- CommandLineNode: dedicated to generate and run external command lines
The desc.Node.onCreated callback is a hook in the Node API for developers to
write custom behavior on a node first initialization.
By being called in the core.Node constructor, this was triggered in several situations
that don't match this idea and with unpredictable side effects (graph loading, node re-creation on undo...).
* Make `onNodeCreated` callback an explicit method on desc.Node.
* Remove the call to node descriptor's `onNodeCreated` callback outside core.Node constructor.
* Trigger this callback on explicit node creation (adding new node to graph, init a graph from a template).
