Move SerialPort and I2C to hardware/.
Fix rotary knob selecting EICAS message.
Fix another Qt parent-child-relationship related bug.

Also add a little startup/shutdown debug logs.
Enable 'set <nil>' button only when PropertyValueNode is selected.
Reorganize module configurator widgets a bit.

TODO ModuleManager::post_module_reload_request().
Identify main source of UI slowliness when PropertyEditor is shown.

It's QTreeWidgetItem::setFirstColumnSpanned() and therefore it's disabled
for now.

Also remove unnecessary reload() of items in their constructors,
and fix unnecessary addTopLevelItem() which is wrong anyway.