TW-93 stable build

This includes changes to the ec2 scripts for separate stable and build machines.

**Assumption**: tw-stable.com will be the host name for the stable server (+1'd by @mirzu)

#### Post-merge work:

- [x] Update the stable build script to track the stable branch

After this is complete, pushes to the stable branch will automatically trigger a rebuild of the stable server. This is easy to disable though if we want the build process to be fully manual.