refactor appReducer: get rid of redundant switch
refactor appReducer: get rid of redundant switch

For some reason just exporint result of `combineReducers` doesn't work:
stores requires a function to be passed.

shri-2015-org/shrimp,Faraser/shrimp,shri-2015-org/shrimp,shri-2015-org/shrimp,Faraser/shrimp