logic: Added indexing mode to reindex incomplete files (issue #493, #496)

* added radio buttons to start indexing dialog
* don't block task scheduler thread while start indexing dialog is visible
* don't force whole project refresh on settings change
* added help button to start indexing dialog explaining indexing modes
* disable unavailable modes when project needs full refresh
* improved label texts on indexing dialogs
* added --incomplete flag to index command of commandline API
* fixed deletion of window stack elements

src/lib_gui/qt/window/QtWindowStack.cpp

@@ -57,7 +57,7 @@ void QtWindowStack::popWindow()
 	if (m_stack.size())
 	{
 		m_stack.back()->hideWindow();
-		delete m_stack.back();
+		m_stack.back()->deleteLater();
 		m_stack.pop_back();
 
 		emit pop();
@@ -93,7 +93,7 @@ void QtWindowStack::clearWindows()
 	for (QtWindowStackElement* window : m_stack)
 	{
 		window->hideWindow();
-		delete window;
+		window->deleteLater();
 	}
 
 	m_stack.clear();