Add custom emojis to the emoji picker (#5052)

app/javascript/mastodon/reducers/custom_emojis.js

@@ -0,0 +1,13 @@
+import { List as ImmutableList } from 'immutable';
+import { STORE_HYDRATE } from '../actions/store';
+
+const initialState = ImmutableList();
+
+export default function statuses(state = initialState, action) {
+  switch(action.type) {
+  case STORE_HYDRATE:
+    return action.state.get('custom_emojis');
+  default:
+    return state;
+  }
+};