Add new EC2 R3 instance types /issue #365

This implements #365.

@dpb587, @mrdavidlaing - in light of the obvious benefits, I've also changed all ES node defaults from the former `m1.large` to the equally priced but more appropriate `r3.large`, with the exception of `node-es-ephemeral-default.template`, because `r3.large` only features very  small 32GB SSD instance storage.

I've **not** changed the defaults in `composite-ci-r53.template` though, thus this wouldn't affect the current deployments yet.