Factor apt-get commands out #243
Description
The way we do apt-get update && apt-get install across many containers is kind of wonky and leads to us generating lots of layers that overlap substantially in content but that can't be cached and reused. @cket @jvivian do you all remember why we wrote all the Dockerfiles this way? Refactoring the apt-get update/install process should save a pretty substantial amount of build time while also reducing image size.