Add new argument to Application::newDocument() to create a temporary
document. Also exposed to Python API App.newDocument() with a named
argument 'temp'.
The temporary document is marked with status bit 'TempDoc'. The user
will not be prompt for saving when closing. The undo/redo is disabled.
The AutoSaver skips it. And the tree view will not show it.
PropertyXLink allows linking to/from object within a temporary document
without saving.
+ avoid warning: QEventLoop: Cannot be used without QApplication
+ avoid warning: QObject::startTimer: Timers can only be used with threads started with QThread
'QString& QString::vsprintf(const char*, __va_list_tag*)' is deprecated: Use vasprintf(), arg() or QTextStream instead [-Wdeprecated-declarations]
'QString& QString::sprintf(const char*, ...)' is deprecated: Use asprintf(), arg() or QTextStream instead [-Wdeprecated-declarations]