Install or upgrade comby for dev environments

Created by: rvantonder

• Previous to this change, comby was not installed by any script in dev environments, because it was a soft dependency. It is now a more necessary dependency (for a8n and local development), so should be integrated into the ./dev/launch.sh if possible.

• This PR aims to or upgrade comby to the desired version for development environments (i.e., when ./dev/launch.sh runs.

Current assumptions for dev environments:

• The binary distribution does not support anything outside of Mac OS X and Ubuntu Linux.
• The install script will prompt sudo for Ubuntu users because it will try to install to /usr/local/bin. There isn't a convenient assumption to make otherwise; we need to put the binary somewhere that is likely already on the PATH.

Test plan:

Tested behavior on Mac OS X, and ran ./dev/launch.sh with

• comby not installed
• comby installed with an older version
• comby installed with the desired version.

Tested the ./dev/comby-install-or-upgrade.sh on ubuntu with the same bullets above.