Rework container tree structure

This sets up a few new classes, subclasses of ContainerNode.

This is intended to simplify the current structure in the QualityManager.

Contributes to issue CURA-6600.

cura/Machines/MaterialNode.py

@@ -1,25 +1,19 @@
-# Copyright (c) 2018 Ultimaker B.V.
+# Copyright (c) 2019 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
-from typing import Optional, Dict, Any
-from collections import OrderedDict
-from .ContainerNode import ContainerNode
 
+from typing import TYPE_CHECKING
 
+from cura.Machines.ContainerNode import ContainerNode
+from cura.Machines.QualityNode import QualityNode
+from cura.Machines.VariantNode import VariantNode
+
+if TYPE_CHECKING:
+    from typing import Dict
+
+##  Represents a material in the container tree.
 #
-# A MaterialNode is a node in the material lookup tree/map/table. It contains 2 (extra) fields:
-#  - material_map: a one-to-one map of "material_root_id" to material_node.
-#  - children_map: the key-value map for child nodes of this node. This is used in a lookup tree.
-#
-#
+#   Its subcontainers are quality profiles.
 class MaterialNode(ContainerNode):
-    __slots__ = ("material_map", "children_map")
-
-    def __init__(self, metadata: Optional[Dict[str, Any]] = None) -> None:
-        super().__init__(metadata = metadata)
-        self.material_map = {}  # type: Dict[str, MaterialNode] # material_root_id -> material_node
-
-        # We overide this as we want to indicate that MaterialNodes can only contain other material nodes.
-        self.children_map = OrderedDict()  # type: OrderedDict[str, "MaterialNode"]
-
-    def getChildNode(self, child_key: str) -> Optional["MaterialNode"]:
-        return self.children_map.get(child_key)
+    def __init__(self, container_id, parent: VariantNode) -> None:
+        super().__init__(container_id, parent)
+        self.qualities = {}  # type: Dict[str, QualityNode] # Mapping container IDs to quality profiles.