- Let's just have one header definining export- and visibility-
macros for Calamares. They are still selected based on the
export flags (*_PRO), just defined in one header instead of two.
- The config context object should be set earlier, otherwise
QML code will try binding to a non-existent config already
- Document that QMLViewStep::setConfigurationMap() parent implementation
should be called **last**, at the end of the subclass implementation.
