im: add indication when no text message are present

Change-Id: I3b971d238edd65cdedfca531cfa33420928f9e68
Tuleap: #232

callwidget.cpp

@@ -608,9 +608,21 @@ CallWidget::on_contactMethodComboBox_currentIndexChanged(const QString& number)
                                 SIGNAL(messageInserted(QMap<QString,QString>,ContactMethod*,Media::Media::Direction)),
                                 this,
                                 SLOT(slotAccountMessageReceived(QMap<QString,QString>,ContactMethod*,Media::Media::Direction)));
+        auto messagesPresent = txtRecording->instantMessagingModel()->rowCount() > 0;
+        if (messagesPresent) {
             ui->listMessageView->scrollToBottom();
             txtRecording->setAllRead();
         }
+        ui->listMessageView->setVisible(messagesPresent);
+        ui->noMessagesLabel->setVisible(!messagesPresent);
+        if (not messagesPresent) {
+            QMetaObject::Connection connection = connect(txtRecording->instantMessagingModel(), &QAbstractItemModel::rowsInserted, [&]() {
+                ui->listMessageView->setVisible(messagesPresent);
+                ui->noMessagesLabel->setVisible(!messagesPresent);
+                disconnect(connection);
+            });
+        }
+    }
 }
 
 void

callwidget.ui

@@ -755,6 +755,23 @@
                   </item>
                  </layout>
                 </item>
+                <item alignment="Qt::AlignHCenter|Qt::AlignVCenter">
+                 <widget class="QLabel" name="noMessagesLabel">
+                  <property name="enabled">
+                   <bool>true</bool>
+                  </property>
+                  <property name="font">
+                   <font>
+                    <pointsize>12</pointsize>
+                    <weight>75</weight>
+                    <bold>true</bold>
+                   </font>
+                  </property>
+                  <property name="text">
+                   <string>Start the conversation !</string>
+                  </property>
+                 </widget>
+                </item>
                 <item>
                  <widget class="QListView" name="listMessageView">
                   <property name="sizePolicy">