`license-checker` is a tool that verifies each file has contains a permitted license header.
See https://github.com/ben-clayton/license-checker for more information.
Also add missing licenses to presubmit scripts.
presubmit.sh now runs presubmit-docker.sh using the new radial
docker image which contains various toolchains.
The `/bin/using.sh` bash script exports the `using` bash function
which can be called to configure toolchains at specific versions.
