Update DraggableWindow to use responsive layout

- Use CSS flex to fill out the component's space
- Add @vueuse/core functions to handle drag and event listener cleanup logic

Author: MarkH817

src/components/ChatApp.vue

@@ -7,9 +7,11 @@
       <template v-slot:main>
         <div class="channel d-flex flex-column">
           <ChannelMessages class="flex-grow-1 flex-shrink-1" />
-          <ChatInput class="flex-grow-1 flex-shrink-0" />
         </div>
       </template>
+      <template v-slot:footer>
+        <ChatInput class="flex-grow-1 flex-shrink-0" />
+      </template>
     </DraggableWindow>
   </div>
 </template>

src/components/chat/ChatInput.vue

@@ -40,8 +40,4 @@
   }
 </script>
 
-<style scoped>
-  .chat-input-container {
-    min-height: 5em;
-  }
-</style>
+<style scoped></style>