This commit moves a number of our encrypted credentials stored in
configuration files in this repository to env vars on the web UI. This
will hopefully make it easier to rotate credentials in the future as
well as quickly change them if the need arises. (quicker than landing a
PR that is).

This also updates the travis deployment process to always use the `aws`
command line tool which we're already installing on Linux and should
enable us to avoid all `dpl` gem issues as well as have greater control
over what's going where.