feat: Add major UI components and functionality

This adds a major chunk of UI code to the application covering topic listing,
topic filtering, subtopic browsing, browsing posts by topic, filtering unread
posts, filtering followed posts, sorting posts by recent activity, most activty
and most votes, liking/unliking a post, following/unfollowing a post, listing
comments and replis in a post.

Co-authored-by: Kshitij Sobti <kshitij@sobti.in>

src/components/SelectableDropdown.jsx

@@ -1,36 +1,37 @@
-import { Dropdown } from '@edx/paragon';
+import React from 'react';
 import PropTypes from 'prop-types';
-import React, { useState } from 'react';
+
+import { Dropdown } from '@edx/paragon';
 
 function SelectableDropdown({
-  options, defaultOption, onChange, label,
+  options,
+  onChange,
+  label,
 }) {
-  const [selected, setSelected] = useState(options.find(option => (option.value === defaultOption)));
   return (
     <Dropdown>
-      <Dropdown.Toggle>
-        { label || selected.label }
+      <Dropdown.Toggle variant="link" size="sm">
+        {label}
       </Dropdown.Toggle>
       <Dropdown.Menu>
-        { options
-          .map(option => (
+        {
+          options.map(option => (
             <Dropdown.Item
               type="button"
               key={option.value}
               onClick={
-                    () => {
-                      setSelected(option);
-                      if (onChange) {
-                        onChange(option);
-                      }
-                    }
+                () => {
+                  if (onChange) {
+                    onChange(option);
                   }
+                }
+              }
             >
-              { option.label }
+              {option.label}
             </Dropdown.Item>
-          )) }
+          ))
+}
       </Dropdown.Menu>
-
     </Dropdown>
   );
 }
@@ -42,7 +43,6 @@ SelectableDropdown.propTypes = {
       label: PropTypes.string,
     }),
   ).isRequired,
-  defaultOption: PropTypes.string.isRequired,
   onChange: PropTypes.func,
   label: PropTypes.node,
 };

src/components/index.js

@@ -1 +1,2 @@
-export * from './selectable-dropdown';
+export { default as PostActionsBar } from '../discussions/posts/post-actions-bar/PostActionsBar';
+export { default as SelectableDropdown } from './SelectableDropdown';

src/components/selectable-dropdown/index.js

@@ -1,2 +0,0 @@
-/* eslint-disable import/prefer-default-export */
-export { default as SelectableDropdown } from './SelectableDropdown';