Widget geometry should be saved together with other Settings

Right now widget geometry saving is tied to resizeEvent, hideEvent, moveEvent and closeEvent in OWBaseWidget.

Instead, it should use a mechanic like the one implemented in https://github.com/biolab/orange-widget-base/pull/151. After that's merged:
- [ ] widget geometry should be saved on settingsAboutTobePacked
- [ ] sync_node_properties should also be called when a widget's window is unfocused (intrinsically calls settingsAboutToBePacked)

Start in OWBaseWidget, where geometry saving is currently tied to resizeEvent, hideEvent, moveEvent, and closeEvent. Review the mechanic from pull request #151, then trace settingsAboutTobePacked and sync_node_properties; done means geometry is saved during settings packing and sync_node_properties runs when the widget window is unfocused.

Written by the indexing model from the issue text.