Improve code quality of the JS commands

[fluegelk]

Improve the code quality of the commands in canvas_project/static/js/commands/:

• Reduce code duplication by introducing super classes for shared functionality
• in undoRedoHandler.mjs: replace hard-coded magic number with a class variable for the maximum stack size
• in updateCommands.mjs: validate new attribute values, not just the attribute names
  • Check if this is also necessary in create commands
• Reuse code to generate name of copied objects (related to Implement a counter when duplicating an object #55)