Add mock API and reorg code for clarity

src/state/models/root-store.ts

@@ -5,9 +5,11 @@
 import {Instance, SnapshotOut, types} from 'mobx-state-tree'
 import {createContext, useContext} from 'react'
 import {SessionModel, createDefaultSession} from './session'
+import {MeModel, createDefaultMe} from './me'
 
 export const RootStoreModel = types.model('RootStore').props({
   session: SessionModel,
+  me: MeModel,
 })
 
 export interface RootStore extends Instance<typeof RootStoreModel> {}
@@ -16,6 +18,7 @@ export interface RootStoreSnapshot extends SnapshotOut<typeof RootStoreModel> {}
 export function createDefaultRootStore() {
   return {
     session: createDefaultSession(),
+    me: createDefaultMe(),
   }
 }