Api update

Small API update + get the main window as a raw pointer like the main document and the main document view. May throw a logic_error if no main window is present, i.e. the application is not in its main loop, you should not catch it and let Vivy crash...

src/VivyApplication.cc

@@ -91,3 +91,14 @@ VivyApplication::getMainWindow() const
         throw std::logic_error("No main window in the graphic VivyApplication");
     return mainWindowPtr.get();
 }
+
+/*
+ * @return the current VivyDocument, or null if there isn't one or if the current document is not a VivyDocument
+ */
+VivyDocument *
+VivyApplication::getCurrentVivyDocument() const
+{
+    if (!mainWindowPtr)
+        throw std::logic_error("No main window in the graphic VivyApplication");
+    return dynamic_cast<VivyDocument*>(mainWindowPtr.get()->getCurrentDocument());
+}