[fix] Make subcomponents handle styles passed in by consumer

[haworku]

Describe the bug
Some small subcomponents don't allow the consumer to customize the styles further. Originally we thought folks could just pass their own custom subcomponent in these cases. But it has been brought up a few times as a point of frustration or confusion.

This is a small change to make things more usable for others.

Expected Behavior
These components handle a custom className prop and apply it to the base element along with UWSDS classes. We use classnames package to append classes for this type of thing.

Components with the problem:

• SocialLinks
• Address
• MegaMenu
• Menu
• NavCloseButton