Move automatic Docker imags build from Docker Hub to Travis-CI

[naorlivne]

Expected/Wanted Behavior

After Travis CI runs the unit tests successfully it should build the Docker image & push it to Docker hub.

If branch is master the image tag should be latest else it should be the same as the branch name (can look at TRAVIS_BRANCH envvar in Travis CI to get branch name being built)

Docker Hub should not build the images anymore as it ignores the unit tests failures.

Also the Docker Hub build tag should be removed from the README.md file

Actual Behavior

Docker hub builds the images while Travis CI runs the unit tests, each ignoring what the results of the other is.

[naorlivne]

Added.