[core] Node: Add a sourceCodeFolder property

This property stores the location of the source code for a given node
and is not exposed to the QML side.

meshroom/core/desc/node.py

@@ -1,3 +1,5 @@
+from inspect import getfile
+from pathlib import Path
 import os
 import psutil
 import shlex
@@ -63,6 +65,7 @@ class Node(object):
     def __init__(self):
         super(Node, self).__init__()
         self.hasDynamicOutputAttribute = any(output.isDynamicValue for output in self.outputs)
+        self.sourceCodeFolder = Path(getfile(self.__class__)).parent.resolve().as_posix()
 
     def upgradeAttributeValues(self, attrValues, fromVersion):
         return attrValues