Bumped version to 1.5.3
As a part of the task T50726:
Update the Panel rename code to more generic one
PEP8 cleanup:
Tuple imports and use them for class types
Consistent Scene props definitions
Flake8 reports two variables being unused:
line 345 - scene
line 347 - select_obj
Haven't removed them yet as that needs some clarification
about their purpose
Own mistake in refactor prior to commit to 'main' addon repo...
Also, some general cleanup (getting rid of stupid literal use of '20' as layer num everywhere!)
and fix for 'separator' in layers UI.