Add global banner support (via banner api)

[JasonLovesDoggo]

reqs:

• dynamically fetch banner from api
• if returns more than one, cycle through them (DONT STACK)

[JasonLovesDoggo]

see https://github.com/wlmac/metropolis/blob/8bf520e5fdc2ef995f39afd8d92c863d90e20232/core/templates/core/base.html#L42

but when more than banner exists, cycle through with a sliding ltr animation.

[JasonLovesDoggo]

Please ping json before working on this.

I want to get thoughts on custom timing for diff ones/scrolling text.