Use strings for setting-constants

more clear when inspecting existing settings; also potentially useful
to avoid circular imports (because you may hard-code using strings,
rather than import the constants)

bugsink/app_settings.py

@@ -11,10 +11,10 @@ _MEBIBYTE = 1024 * _KIBIBYTE
 
 
 # CB means "create by"
-CB_ANYBODY = 0
-CB_MEMBERS = 1
-CB_ADMINS = 2
-CB_NOBODY = 3
+CB_ANYBODY = "CB_ANYBODY"
+CB_MEMBERS = "CB_MEMBERS"
+CB_ADMINS = "CB_ADMINS"
+CB_NOBODY = "CB_NOBODY"
 
 
 DEFAULTS = {