Bug 851727 -Responsify powered-by page
Migrate /projects/powered-by.html to bedrock. Bug 851727.

UI cleanup. URL redirects added (review needed).

Built on @retornam's initial branch.
Updated img alt attr, fixed phone view.
Updated URL rewrites (thanks @pmclanahan).
Updated URLs/rewrites to replace /projects/ with /about/.
Updated rewrite rule to handle trailing slash.