Extract a few changes from the Mithril 2 upgrade (#2262)

* Fix closing the composer with ESC key

Regression from #2161.

* Remove obsolete method

Regression from #2162.

* Mark method as protected

* Fade in posts in post stream using CSS

This also avoids a double-fade from the JavaScript code, which was
probably introduced in #2160.

* Fix fadeIn for post stream items

Co-authored-by: Alexander Skvortsov <sasha.skvortsov109@gmail.com>

js/src/common/components/Modal.js

@@ -105,8 +105,6 @@ export default class Modal extends Component {
     this.$('form').find('input, select, textarea').first().focus().select();
   }
 
-  onhide() {}
-
   /**
    * Hide the modal.
    */