Promoting a QWidget does not easily work with stock template

Steps:

• Create CMake based Widget App via templates
• Add PushButton to mainwindow.ui
• "Promote To" => give it some class name and header file name
• Add a new header file with the choosen name to the project
• Try to build

Expected:

• The header file is found during build ( will still fail build because class is missing )

Actual:

• The header file is not found because the source folder is not added as a "target_include_directory"