Preserve hashtags in threaded mode (fixes #584)

app/javascript/flavours/glitch/reducers/compose.js

@@ -113,6 +113,12 @@ function apiStatusToTextMentions (state, status) {
   )).join('');
 }
 
+function apiStatusToTextHashtags (state, status) {
+  return ImmutableOrderedSet([]).union(status.tags.map(
+    ({ name }) => `#${name} `
+  )).join('');
+}
+
 function clearAll(state) {
   return state.withMutations(map => {
     map.set('text', '');
@@ -133,7 +139,9 @@ function clearAll(state) {
 
 function continueThread (state, status) {
   return state.withMutations(function (map) {
-    map.set('text', apiStatusToTextMentions(state, status));
+    let text = apiStatusToTextMentions(state, status);
+    text = text + apiStatusToTextHashtags(state, status);
+    map.set('text', text);
     if (status.spoiler_text) {
       map.set('spoiler', true);
       map.set('spoiler_text', status.spoiler_text);