Changed Themes and Assets folder

[enesyurtlu]

Changed assets and themes folder to use it like "wordpress theming"

[danhunsaker]

This behavior is already supported by defining your theme's paths according to WordPress conventions in your theme.json or config/themes.php. The proposed changes obliterate this capability, and force the WordPress style, which is not desirable in many use cases, and is a backward compatibility break in any case.