Implement hotkeys for web UI (#5164)

* Fix #2102 - Implement hotkeys

Hotkeys on status list:

- r to reply
- m to mention author
- f to favourite
- b to boost
- enter to open status
- p to open author's profile
- up or k to move up in the list
- down or j to move down in the list
- 1-9 to focus a status in one of the columns
- n to focus the compose textarea
- alt+n to start a brand new toot
- backspace to navigate back

* Add navigational hotkeys

The key g followed by:

- s: start
- h: home
- n: notifications
- l: local timeline
- t: federated timeline
- f: favourites
- u: own profile
- p: pinned toots
- b: blocked users
- m: muted users

* Add hotkey for focusing search, make escape un-focus compose/search

* Fix focusing notifications column, fix hotkeys in compose textarea

app/javascript/mastodon/components/status_list.js

@@ -25,18 +25,45 @@ export default class StatusList extends ImmutablePureComponent {
     trackScroll: true,
   };
 
+  handleMoveUp = id => {
+    const elementIndex = this.props.statusIds.indexOf(id) - 1;
+    this._selectChild(elementIndex);
+  }
+
+  handleMoveDown = id => {
+    const elementIndex = this.props.statusIds.indexOf(id) + 1;
+    this._selectChild(elementIndex);
+  }
+
+  _selectChild (index) {
+    const element = this.node.node.querySelector(`article:nth-of-type(${index + 1}) .focusable`);
+
+    if (element) {
+      element.focus();
+    }
+  }
+
+  setRef = c => {
+    this.node = c;
+  }
+
   render () {
     const { statusIds, ...other } = this.props;
     const { isLoading } = other;
 
     const scrollableContent = (isLoading || statusIds.size > 0) ? (
       statusIds.map((statusId) => (
-        <StatusContainer key={statusId} id={statusId} />
+        <StatusContainer
+          key={statusId}
+          id={statusId}
+          onMoveUp={this.handleMoveUp}
+          onMoveDown={this.handleMoveDown}
+        />
       ))
     ) : null;
 
     return (
-      <ScrollableList {...other}>
+      <ScrollableList {...other} ref={this.setRef}>
         {scrollableContent}
       </ScrollableList>
     );