accountsReducer: Make REALM_ADD store feature level in Redux.

As we have included the feature level in REALM_ADD and
Account type in the previous commits. Now, we store the
feature level in Redux on REALM_ADD.

Part of #4049.

Author: hashirsarwar

src/account/__tests__/accountsReducer-test.js

@@ -31,7 +31,6 @@ describe('accountsReducer', () => {
         email: '',
         apiKey: '',
         realm: 'https://new.realm.org',
-        zulipFeatureLevel: null, // Will be removed in an upcoming commit.
       });
 
       const action = deepFreeze({

src/account/accountsReducer.js

@@ -21,6 +21,7 @@ const realmAdd = (state, action) => {
   if (accountIndex !== -1) {
     const newAccount = {
       ...state[accountIndex],
+      zulipFeatureLevel: action.zulipFeatureLevel,
       zulipVersion: action.zulipVersion,
     };
     return [newAccount, ...state.slice(0, accountIndex), ...state.slice(accountIndex + 1)];
@@ -32,7 +33,7 @@ const realmAdd = (state, action) => {
       apiKey: '',
       email: '',
       ackedPushToken: null,
-      zulipFeatureLevel: null,
+      zulipFeatureLevel: action.zulipFeatureLevel,
       zulipVersion: action.zulipVersion,
     },
     ...state,