Ability to change None for dimensions

[#1]

We would like to have the ability to override the None default for dimensions to something more meaningful.  For example, we have the following referrer #'s:

	Page Views
Internal Referrer	213,923
External Referrer	35,718
None	736

We would like to show it as this:

	Page Views
Internal Referrer	213,923
External Referrer	35,718
Referrer Not Available	736

We probably can perform a bunch of rename dimensions but would prefer to leverage the Default option in transformation configruations.