DP: Bandwidth Documentation Sunset

[inertia186]

As an app developer, I would like to find appropriate historical information about the concept known as "bandwidth", so that I know I'm not suffering from The Mandela Effect.

Also see: https://github.com/steemit/steem/issues/3029#issuecomment-428404844

AC

• [x] replace all mentions of bandwidth with RC, where appropriate
• [x] all references of bandwidth are relegated to historical mentions, where appropriate
• [x] fields no longer returned in API calls are removed from examples
• [x] concepts, history & useful articles ('breadcrumbs?') section. Brief article in the section about bandwidth being replaced with RC