Adds function to generate context menu with available contents.

Refactors some auto-keywords to its real class names.
Paints drop location based on cursors drop area indicator.
Waits a few pixel before moving tab from SectionWidget.

AdvancedDockingSystemDemo/src/mainwindow.cpp

@@ -57,6 +57,7 @@ MainWindow::MainWindow(QWidget *parent) :
 {
 	ui->setupUi(this);
 	ui->mainToolBar->hide();
+	ui->statusBar->hide();
 	QObject::connect(ui->actionAddSectionContent, &QAction::triggered, this, &MainWindow::onActionAddSectionContentTriggered);
 
 	// CREATE SOME TESTING DOCKS