On-demand auth

* auth block was moved to comment form
* if comments on page read only auth form shows in old place
* comment value in form will be saved between refreshes (it is side effect form saving comment value between unauth and auth states)

frontend/app/components/thread/thread.scss

@@ -1,6 +1,5 @@
 .thread {
   position: relative;
-  overflow: hidden;
 }
 
 .thread_indented {

frontend/app/components/thread/thread.tsx

@@ -24,8 +24,9 @@ interface Props {
 }
 
 const commentSelector = (id: string) => (state: StoreState) => {
-  const { theme, comments, childComments } = state;
-  const comment = comments[id];
+  const { theme, comments } = state;
+  const { allComments, childComments } = comments;
+  const comment = allComments[id];
   const childs = childComments[id];
   const collapsed = getThreadIsCollapsed(comment)(state);