add: added the class constructor for the difficulty dropdown component

Author: kiing-dom

options/difficulyDropdown.js

@@ -0,0 +1,9 @@
+class DifficultyDropdown {
+    constructor(container, difficulties, onChange) {
+        this.container = container;
+        this.difficulties = difficulties;
+        this.onChange = onChange;
+        this.selectedDifficulty = 'all';
+        this.filteredDifficulties = ['all', ...difficulties];
+    }
+}

options/options.html

@@ -35,6 +35,7 @@ <h2>All Solved Problems</h2>
                         <option value="recent-desc">Most recently solved</option>
                         <option value="recent-asc">Least recently solved</option>
                     </select>
+                    <div id="difficultyDropdownContainer"></div>
                 </div>
                 <div id="problemsList"></div>
             </section>