Create Makefile to build and push Docker image to one's own image registry

Right now, there is no automated means in the project (besides the Travis file) to build, tag, and push Kubesweeper to one's image repository (such as Docker Trusted Registry) from a local machine. One way to do this is in a Makefile.

Start by reading the existing Travis file and the project’s Docker build configuration to understand how Kubesweeper is built and tagged. Add a Makefile entry point for building, tagging, and pushing the image to a user-selected registry, then verify the commands work with a local Docker setup.

Written by the indexing model from the issue text.