3MF files are now correctly loaded inside the build platform

CURA-382

plugins/3MFReader/ThreeMFReader.py

@@ -141,12 +141,12 @@ class ThreeMFReader(MeshReader):
         flip_matrix = Matrix()
         flip_matrix._data[1, 1] = 0
         flip_matrix._data[1, 2] = 1
-        flip_matrix._data[2, 1] = 1
+        flip_matrix._data[2, 1] = -1
         flip_matrix._data[2, 2] = 0
         result.setTransformation(flip_matrix)
         if global_container_stack:
             translation = Vector(x=-global_container_stack.getProperty("machine_width", "value") / 2, z=0,
-                                 y=global_container_stack.getProperty("machine_depth", "value") / 2)
+                                 y=-global_container_stack.getProperty("machine_depth", "value") / 2)
             result.translate(translation)
         result.setEnabled(False) # The result should not be moved in any way, so disable it.
         return result