Adding upvote and downvote plugins and sorting plugins for each

plugins/talk-plugin-downvote/client/components/DownvoteButton.css

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+.container {
+  display: inline-block;
+}
+
+.button {
+  color: #2a2a2a;
+  margin: 5px 10px 5px 0px;
+  background: none;
+  padding: 0px;
+  border: none;
+  font-size: inherit;
+  vertical-align: middle;
+
+  &:hover {
+    color: #767676;
+    cursor: pointer;
+  }
+
+  &.downvoted {
+    color: #cc0000;
+
+    &:hover {
+      color: #ff3232;
+      cursor: pointer;
+    }
+  }
+}
+
+.icon {
+  font-size: 12px;
+  padding: 0 3px;
+}
+
+@media (max-width: 425px) {
+  .label {
+    display: none;
+  }
+}
+

plugins/talk-plugin-downvote/client/components/DownvoteButton.js

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+import React from 'react';
+import Icon from './Icon';
+import styles from './DownvoteButton.css';
+import { withReaction } from 'plugin-api/beta/client/hocs';
+import cn from 'classnames';
+
+const plugin = 'talk-plugin-downvote';
+
+class DownvoteButton extends React.Component {
+  handleClick = () => {
+    const {
+      postReaction,
+      deleteReaction,
+      showSignInDialog,
+      alreadyReacted,
+      user,
+    } = this.props;
+
+    // If the current user does not exist, trigger sign in dialog.
+    if (!user) {
+      showSignInDialog();
+      return;
+    }
+
+    if (alreadyReacted) {
+      deleteReaction();
+    } else {
+      postReaction();
+    }
+  };
+
+  render() {
+    const { count, alreadyReacted } = this.props;
+    return (
+      <div className={cn(styles.container, `${plugin}-container`)}>
+        <button
+          className={cn(
+            styles.button,
+            {
+              [`${
+                styles.downvoted
+              } talk-plugin-downvote-downvoted`]: alreadyReacted,
+            },
+            `${plugin}-button`
+          )}
+          onClick={this.handleClick}
+        >
+          <Icon className={cn(styles.icon, `${plugin}-icon`)} />
+          <span className={cn(`${plugin}-count`)}>{count > 0 && count}</span>
+        </button>
+      </div>
+    );
+  }
+}
+
+export default withReaction('downvote')(DownvoteButton);

plugins/talk-plugin-downvote/client/components/Icon.js

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+import React from 'react';
+import cn from 'classnames';
+
+export default ({ className }) => (
+  <i
+    className={cn('fa', 'fa-arrow-circle-down', className)}
+    aria-hidden="true"
+  />
+);