Support banner

This page will accommodate the new adapter design, to support banner (display) type media, in our adapter

• add banner type to supported media type

• update endpoint to new hb-multi

• create the new imp object to send

• change GET request to POST (and verify old behavior is not affected and destroyed)

• isBidRequestValid - does is need to be changed? is there a different validation for banners?

• build request - what's needed for a banner request compared to video

• Find what's common between video and banner request and reuse data when building object