Allow user to close a conversation (chatbox)

One step ahead in the memory game! This commit closes #12 (closes,
get it? :P)

src/routes/Chat.svelte

@@ -1,6 +1,8 @@
 <script lang="ts">
   import Text from '../components/Text.svelte'
   import ChatMessage from '../components/ChatMessage.svelte'
+  import OptionsMenu from '../components/OptionsMenu.svelte'
+  import ListItem from '../components/ListItem.svelte'
   import Input from '../components/Input.svelte'
 
   import { onMount } from 'svelte'
@@ -22,6 +24,10 @@
   let chatListEl
   let composeBox
 
+  // Whether the options menu is visible or not
+  let optionsMenuVisible = false
+
+
   $: title = chatbox?.attributes?.nickname || chatbox?.attributes?.id || params.chatID || 'Convo'
   $: titleStore.update(() => title)
 
@@ -90,7 +96,9 @@
     }
 
     k.right.label = 'Options'
-    k.right.callback = () => {}
+    k.right.callback = () => {
+      optionsMenuVisible = !optionsMenuVisible
+    }
 
     return k
   })
@@ -183,6 +191,14 @@
     onComposeBoxUpdate()
   }
 
+  // Function to close a conversation
+  function closeChat() {
+    chatbox.close().then(() => {
+      push('/messages')
+    })
+  }
+
+  // Get it all running!
   onMount(() => {
     // Initialise the chatbox
     chatbox = _converse.chatboxes.get(params.chatID)
@@ -223,6 +239,15 @@
   />
 </div>
 
+{#if optionsMenuVisible}
+<OptionsMenu title="Options">
+  <ListItem
+    text="Close conversation"
+    onclick={closeChat}
+  />
+</OptionsMenu>
+{/if}
+
 <style>
   .compose-box {
     height: 8rem;