Cache relationships in API (#6482)

* Cache relationships in API

* Fetch relationships for search results in UI

* Only save one account's maps in each cache item

app/javascript/mastodon/actions/search.js

@@ -1,4 +1,5 @@
 import api from '../api';
+import { fetchRelationships } from './accounts';
 
 export const SEARCH_CHANGE = 'SEARCH_CHANGE';
 export const SEARCH_CLEAR  = 'SEARCH_CLEAR';
@@ -38,6 +39,7 @@ export function submitSearch() {
       },
     }).then(response => {
       dispatch(fetchSearchSuccess(response.data));
+      dispatch(fetchRelationships(response.data.accounts.map(item => item.id)));
     }).catch(error => {
       dispatch(fetchSearchFail(error));
     });