Move PurgeDialog to Chat. Improve robustness of purge.

Also, set message retention to 60 seconds and make sure online user "forget"s room.

src/components/Chat.vue

@@ -3,10 +3,12 @@
     <ChatHeaderPrivate class="chat-header flex-grow-0 flex-shrink-0"
       v-on:header-click="onHeaderClick"
       v-on:view-room-details="viewRoomDetails"
+      v-on:purge="showPurgeConfirmation = true"
       v-if="!useFileModeNonAdmin && $matrix.isDirectRoom(room)" />
       <ChatHeader class="chat-header flex-grow-0 flex-shrink-0"
       v-on:header-click="onHeaderClick"
       v-on:view-room-details="viewRoomDetails"
+      v-on:purge="showPurgeConfirmation = true"
       v-else-if="!useFileModeNonAdmin" />
     <AudioLayout ref="chatContainer" class="auto-audio-player-root" v-if="useVoiceMode" :room="room"
       :events="events" :autoplay="!showRecorder"
@@ -321,6 +323,9 @@
       :room="room"
       @close="showProfileDialog = false"
     />
+
+    <!-- PURGE ROOM POPUP -->
+    <PurgeRoomDialog :show="showPurgeConfirmation" :room="room" @close="showPurgeConfirmation = false" />
   </div>
 </template>
 
@@ -349,6 +354,7 @@ import AudioLayout from "./AudioLayout.vue";
 import FileDropLayout from "./file_mode/FileDropLayout";
 import roomTypeMixin from "./roomTypeMixin";
 import roomMembersMixin from "./roomMembersMixin";
+import PurgeRoomDialog from "../components/PurgeRoomDialog";
 
 const sizeOf = require("image-size");
 const dataUriToBuffer = require("data-uri-to-buffer");
@@ -400,7 +406,8 @@ export default {
     CreatePollDialog,
     AudioLayout,
     FileDropLayout,
-    UserProfileDialog
+    UserProfileDialog,
+    PurgeRoomDialog,
   },
 
   data() {
@@ -483,7 +490,8 @@ export default {
        * A timer to handle message retention/auto deletion
        */
       retentionTimer: null,
-      showProfileDialog: false
+      showProfileDialog: false,
+      showPurgeConfirmation: false,
     };
   },