warning on preview unavailable during call

Change-Id: I8f0e38a9a7ad5593550c71384b44b15eb78903a1
Tuleap: #277

configurationwidget.cpp

@@ -108,7 +108,12 @@ ConfigurationWidget::showEvent(QShowEvent *event) {
     QWidget::showEvent(event);
     if (ui->tabWidget->currentIndex() == 1
             && CallModel::instance().getActiveCalls().size() == 0) {
+        ui->previewUnavailable->hide();
+        ui->videoView->show();
         Video::PreviewManager::instance().startPreview();
+    } else {
+        ui->previewUnavailable->show();
+        ui->videoView->hide();
     }
 }
 

configurationwidget.ui

@@ -7,7 +7,7 @@
     <x>0</x>
     <y>0</y>
     <width>558</width>
-    <height>433</height>
+    <height>475</height>
    </rect>
   </property>
   <property name="sizePolicy">
@@ -401,6 +401,20 @@
            </property>
           </widget>
          </item>
+         <item alignment="Qt::AlignHCenter|Qt::AlignVCenter">
+          <widget class="QLabel" name="previewUnavailable">
+           <property name="font">
+            <font>
+             <pointsize>13</pointsize>
+             <weight>75</weight>
+             <bold>true</bold>
+            </font>
+           </property>
+           <property name="text">
+            <string>Preview unavailable during call</string>
+           </property>
+          </widget>
+         </item>
          <item>
           <widget class="QLabel" name="cameraPreviewLabel">
            <property name="maximumSize">