Revert "Cleanup: Use the @ syntax for some properties"

This reverts commit d211e0de47114d3e2b8bc31ef0f7f9fc24355fb5.
Revert "Cleanup: Rename isblank to is_blank and convert to property"

This reverts commit 199cf7926fffd5dd7ee1838cb0de0f97bf9032dd.

This gets us back to before we started altering the TTK API and deprecating
the changed methods.
Add deprecated decorator to easily mark deprecated functions and methods
Use the new deprecated decorator instead of custom deprecation code