code cleanup (split constants into a folder)

[Lendemor]

Reorganize the constants folder to split them into logical module.

(Also make use of SimpleNamespace to group some constants together.)

[masenf]

I think the namespace classes themselves should be TitleCase like you'd expect for a class. but otherwise the categorization and breakdown looks just right.

[Lendemor]

I think the namespace classes themselves should be TitleCase like you'd expect for a class. but otherwise the categorization and breakdown looks just right.

Personally I think it's neater to have them in UPPER_CASE because when seeing them in the end code it's immediately clear that they are "constant groups" rather than utility/core classes.

(i.e a DefaultPage could be confused with a default page object that can be instantiated, whereas I find it clearer that DEFAULT_PAGE is not a object to be instantiated).