Create presubmit.yml for Bazel continuous integration (#3723)

* Create presubmit.yml

This (+ a PR in will put
make Bazel changes that break Kythe visible to the Bazel team before a
release is cut.

This just builds for Ubuntu 18.04, but can be expanded to do windows,
osx, or ubuntu 16.04. For now I want to start small and see if we can get
the two to just talk to each other.

* Respond to reviewer comments
1 file changed