make popups more predictable

Related to https://github.com/ArcBees/GWTP/issues/554
We used them for a while and are now aiming to remove them for a reason. I don't think final on params/variables add a lot to code readability, much less on documentation. Rather they introduce noise that you need to mentally skip when reading code. Checkstyle throws a warning (or it should only be a warning) for parameter assignment. This is a bad practice, but in the end we don't think adding final is doing more harm to code readability.