BIM: Fix imports of Python importers

src/Mod/BIM/bimcommands/BimIfcExplorer.py

@@ -252,7 +252,7 @@ class BIM_IfcExplorer:
     def insert(self):
         "inserts selected objects in the active document"
 
-        import importIFC
+        from importers import importIFC
         from PySide import QtCore, QtGui
 
         doc = FreeCAD.ActiveDocument

src/Mod/BIM/bimcommands/BimLibrary.py

@@ -588,7 +588,7 @@ class BIM_Library_TaskPanel:
 
             todo.delay(self.reject, None)
         elif ext == ".ifc":
-            import importIFC
+            from importers import importIFC
 
             importIFC.ZOOMOUT = False
             importIFC.insert(path, FreeCAD.ActiveDocument.Name)