Use the master request from the stack

I think this solves #84, though not sure if it will cause problems with ESI.  Can anyone confirm?

Always using the master request from the request stack means that we're only concerned about the locale of the controlling page.

Sub-requests do not have access to the route which causes TargetInformationBuilder to throw a RouteNotFoundException on line 105.  This ensures that we are using the master request which does have access to the route.  Another approach may be to refactor TargetInfomrationBuilder, though I get a little bit lost in there.

Regardless we should probably migrate over to the request stack since retrieving the request as a service will be removed in 3.0