Add dynamic pipeline template (YAML and Python)

Provide a YAML template that a project can include in order to take a base pipeline configuration YAML file in the project repo, parse the configuration into a Python dictionary (embedding other included templates), and run Python code in the project repo that alters the configuration. The final configuration is then used to generate a new (dynamic) pipeline, which runs as a child pipeline.

Also include a module of helper function(s) (currently only merge_dict() for deep merging of dictionaries) that a project can use to help in altering the dynamic pipeline configuration.

Documentation about GitLab dynamic pipelines can be found at: https://docs.gitlab.com/ee/ci/parent_child_pipelines.html

Closes #15 (closed)