removed EXPOSE cmd in frontend's Dockerfile.dev and added empty dependencies to CI stages that don't need artifacts for efficiency

- simplified branch and image tagging in CI
- minor cleanup of CI scripts

This reverts commit 68320db2.

- Added PATH_PREFIX variable to build stage to handle dockerfiles at paths other than /services
- removed .unit-test template from .gitlab-ci.yml because it was duplicated

Added run-tests.sh script to each service to run our package tester to enable us
to run unit tests from the cmdline and CI
Refactored makefile's make test script to call run-tests.sh in each image

Added Push stage to push docker images to our registry when PR is merged