Added stub workspace reader

CURA-1263

plugins/3MFReader/ThreeMFWorkspaceReader.py

@@ -0,0 +1,12 @@
+from UM.Workspace.WorkspaceReader import WorkspaceReader
+
+
+##    Base implementation for reading 3MF workspace files.
+class ThreeMFWorkspaceReader(WorkspaceReader):
+    def __init__(self):
+        super().__init__()
+
+    def preRead(self, file_name):
+        return WorkspaceReader.PreReadResult.accepted
+        # TODO: Find 3MFFileReader so we can load SceneNodes
+        # TODO: Ask user if it's  okay for the scene to be cleared

plugins/3MFReader/__init__.py

@@ -2,10 +2,11 @@
 # Cura is released under the terms of the AGPLv3 or higher.
 
 from . import ThreeMFReader
-
+from . import ThreeMFWorkspaceReader
 from UM.i18n import i18nCatalog
 catalog = i18nCatalog("cura")
 
+
 def getMetaData():
     return {
         "plugin": {
@@ -20,8 +21,17 @@ def getMetaData():
                 "extension": "3mf",
                 "description": catalog.i18nc("@item:inlistbox", "3MF File")
             }
+        ],
+        "workspace_reader":
+        [
+            {
+                "extension": "3mf",
+                "description": catalog.i18nc("@item:inlistbox", "3MF File")
+            }
         ]
     }
 
+
 def register(app):
-    return { "mesh_reader": ThreeMFReader.ThreeMFReader() }
+    return {"mesh_reader": ThreeMFReader.ThreeMFReader(),
+            "workspace_reader": ThreeMFWorkspaceReader.ThreeMFWorkspaceReader()}