Merge changes Ic5b222a4,If3eb5588,I7754b4a5,I646e605c,I47eeefb5

* changes:
  [apps/graph] Fix bug: select the right column title when hiding and displaying derivative column in value page
  [escher] In container, avoir useless switchApp
  [poincare] Change name DisplayMode -> FloatDisplayMode
  [apps/shared] Avoid container casting when possible
  [apps/shared] Correct bug in checksum

escher/src/container.cpp

@@ -10,6 +10,9 @@ Container::Container() :
 }
 
 void Container::switchTo(App * app) {
+  if (m_activeApp == app) {
+    return;
+  }
   if (m_activeApp) {
     m_activeApp->willBecomeInactive();
   }