Fix layout of the topics editing form (#4971)

* Fix layout of the topic edit.

- made right-hand column wider so that it has enough space for "Done" button.

- fixed issue that jQuery's .show() breaks functionality of the Semantic UI Grid.

* Improve switching visibility of the topic edit

Changes to support old browsers that doesn't support 'flex' keyword.

- Removed style "display: none" from index.css so that
  the grid can be displayed without specifying new "display" style.

- Added style "display:none" to the grid element in HTML template
  as the initial style.

- In index.js, visibility of the grid element is changed by
  set "display:none" style to the element or removing it from the element.

public/less/_repository.less

@@ -1805,7 +1805,6 @@ tbody.commit-list {
 
 #topic_edit {
     margin-top:5px;
-    display: none;
 }
 
 #repo-topic {