Use an enum for switching focus instead of hard coded numbers

nw/constants/__init__.py

@@ -6,7 +6,7 @@ from nw.constants.constants import (
 )
 from nw.constants.enum import (
     nwAlert, nwDocAction, nwItemClass, nwItemLayout, nwItemType, nwOutline,
-    nwDocInsert
+    nwDocInsert, nwWidget
 )
 
 __all__ = [
@@ -28,4 +28,5 @@ __all__ = [
     "nwItemType",
     "nwOutline",
     "nwDocInsert",
+    "nwWidget",
 ]

nw/constants/enum.py

@@ -112,6 +112,15 @@ class nwAlert(Enum):
 
 # END Enum nwAlert
 
+class nwWidget(Enum):
+
+    TREE    = 1
+    EDITOR  = 2
+    VIEWER  = 3
+    OUTLINE = 4
+
+# END Enum nwWidget
+
 class nwOutline(Enum):
 
     TITLE  = 0