Remove RecipeResource, move substitutable
This removes the RecipeResource class from the recipe. Since it is removed, the substitutable property was moved to ResourceSpecification. The relationship recipeFlowResource was changed to resourceConformsTo, in order to directly reference ResourceSpecification from RecipeFlow.
I'm not sure I did the bridging right, please review. Perhaps resourceConformsTo shouldn't be in the recipe.gql file, but only in bridging?