Pygubu

* Hotfix, reset code tab on load file.

* Use a lighter code formatter. Removed black, use autopep8. refs alejandroautalan/pygubu-designer152
* Fix AttributeError: 'Dialog' object has no attribute 'update_idletasks' when pressing F5
* Add example integration with python zipapp module. refs alejandroautalan/pygubu269

* New selected indicator in preview.
* Completed menu support for code generator (issue alejandroautalan/pygubu-designer103)
* Decluttering for widget IDs (issue alejandroautalan/pygubu-designer117)

* Hotfix: Fix template path in preferences window alejandroautalan/pygubu-designer147 (jrezai)

* Changed project structure to use src folder.
* Added internal cursor property editor.
* Adapted code to use pygubu plugin engine
* Merged pull request alejandroautalan/pygubu-designer138 from jrezai/master

* Added more examples
* Fix: 'filedialog.askopenfilename' is blocked by 'preferences.dialog' (larryw3i).
* Translations for pygubu strings in pygubu-designer (larryw3i)