222: removed inheritance of ALL item modifiers

[evanmwillhite]

#222: Children menu items incorrectly inheriting ALL item modifiers

Description:
Implements the great patch proposed in #222 (comment) to ensure original menu item modifiers get passed down but not ones that are specific to a specific level (e.g., main-menu__item--with-sub)

To review:

• Before checking out this branch, view the source of the Main Menu and verify that every dropdown child incorrectly has the class main-menu__item--with-sub
• Checkout this branch and verify that only the dropdown items with a dropdown below them have that class.

[ModulesUnraveled]

I've been using this on projects.