RB.BaseResource and RB.ReviewReply both mix in other classes, but

were doing so after the call to .extend(). This meant that the mixin

wasn't part of the original state going into the prototype. While not a

problem in Backbone, it does impact Spina, as the wrong prototype ends

up being used.
This change fixes up these two classes to apply mixins the same way that

other classes do, inline in a call to .extend().

Unit tests pass.
Tested this with the in-progress Spina 2 work, which supports .extend().