Gui: support in-place editing

The link support means that an object can now appear in more than one
places, and even inside a document different from its own. This patch
adds support for in-place editing, meaning that the object can be edited
at correct place regardless where it is.

See [here](https://git.io/fjPIk) for more info about the relavent APIs.

This patch includes two example of modifications to support in-place
editing. One is the ViewProviderDragger, which simply adds the dragger
node to editing root node by calling
View3DInventorViewer::setupEditingRoot(dragger). The other much more
complex one is ViewProviderSketch which calls setupEditingRoot(0) to
transfer all its children node into editing root. ViewProviderSketch
also includes various modifications to command invocation, because we
can no longer assume the active document is the owner of the editing
object.

This patch also includes necessary modification of the 'Show' module to
support in-place editing.

src/Gui/Application.cpp

@@ -142,6 +142,7 @@ struct ApplicationP
 {
     ApplicationP() :
     activeDocument(0L),
+    editDocument(0L),
     isClosing(false),
     startingUp(true)
     {
@@ -158,6 +159,7 @@ struct ApplicationP
     std::map<const App::Document*, Gui::Document*> documents;
     /// Active document
     Gui::Document*   activeDocument;
+    Gui::Document*  editDocument;
     MacroManager*  macroMngr;
     /// List of all registered views
     std::list<Gui::BaseView*> passive;
@@ -863,6 +865,25 @@ Gui::Document* Application::activeDocument(void) const
     return d->activeDocument;
 }
 
+Gui::Document* Application::editDocument(void) const
+{
+    return d->editDocument;
+}
+
+Gui::MDIView* Application::editViewOfNode(SoNode *node) const
+{
+    return d->editDocument?d->editDocument->getViewOfNode(node):0;
+}
+
+void Application::setEditDocument(Gui::Document *doc) {
+    if(!doc) 
+        d->editDocument = 0;
+    for(auto &v : d->documents)
+        v.second->_resetEdit();
+    d->editDocument = doc;
+    getMainWindow()->updateActions();
+}
+
 void Application::setActiveDocument(Gui::Document* pcDocument)
 {
     if (d->activeDocument == pcDocument)

src/Gui/Application.h

@@ -146,6 +146,11 @@ class GuiExport Application
     Gui::Document* activeDocument(void) const;
     /// Set the active document
     void setActiveDocument(Gui::Document* pcDocument);
+    /// Getter for the editing document
+    Gui::Document* editDocument(void) const;
+    Gui::MDIView* editViewOfNode(SoNode *node) const;
+    /// Set editing document, which will reset editing of all other document
+    void setEditDocument(Gui::Document* pcDocument);
     /** Retrieves a pointer to the Gui::Document whose App::Document has the name \a name.
     * If no such document exists 0 is returned.
     */
@@ -250,6 +255,7 @@ class GuiExport Application
     static PyObject* sActiveView               (PyObject *self,PyObject *args);
     static PyObject* sActivateView             (PyObject *self,PyObject *args);
     static PyObject* sGetDocument              (PyObject *self,PyObject *args);
+    static PyObject* sEditDocument             (PyObject *self,PyObject *args);
 
     static PyObject* sDoCommand                (PyObject *self,PyObject *args);
     static PyObject* sDoCommandGui             (PyObject *self,PyObject *args);

src/Gui/ApplicationPy.cpp

@@ -165,6 +165,9 @@ PyMethodDef Application::Methods[] = {
   {"activateView", (PyCFunction)Application::sActivateView, METH_VARARGS,
    "activateView(type)\n\n"
    "Activate a view of the given type of the active document"},
+  {"editDocument", (PyCFunction)Application::sEditDocument, METH_VARARGS,
+   "editDocument() -> object or None\n\n"
+   "Return the current editing document or None if no one exists" },
   {"getDocument",             (PyCFunction) Application::sGetDocument, METH_VARARGS,
    "getDocument(string) -> object\n\n"
    "Get a document by its name"},
@@ -203,6 +206,20 @@ PyMethodDef Application::Methods[] = {
   {NULL, NULL, 0, NULL}		/* Sentinel */
 };
 
+PyObject* Gui::Application::sEditDocument(PyObject * /*self*/, PyObject *args)
+{
+	if (!PyArg_ParseTuple(args, ""))     // convert args: Python->C 
+		return NULL;                       // NULL triggers exception 
+
+	Document *pcDoc = Instance->editDocument();
+	if (pcDoc) {
+		return pcDoc->getPyObject();
+	}
+	else {
+		Py_Return;
+	}
+}
+
 PyObject* Gui::Application::sActiveDocument(PyObject * /*self*/, PyObject *args)
 {
     if (!PyArg_ParseTuple(args, ""))