[development] Forms APIing our theme system

[Vladimir Zlatanov]

> Here's another place the Forms API shines. We pass a well defined, 
> structured data set. Clean separation of content and presentation.
That is so true.....

> While we're making changes, we could consider a full move to a Forms API 
> approach for all data passed to theming. Likely doing so would greatly 
> simplify the theming system.
it won't solve the defaults problems