Added fromWhere method

[bsutton]

Given the whole dependency overriding thing it may be useful to provide a method that tells the user where we are going to get the key from.

This would primarily be for debugging purposes.

The method would return the name of the scope the the key would be fetched from.

One of:

Scope: debugName - maybe the nesting level e.g. 1 for the nearset scope, 2 for the one above it.
GlobalScope: debugName
ScopeKey.withDefault
use: default