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/.
Merge pull request #702 from jpetto/Bug851727

Migrate /projects/powered-by.html to bedrock