Implement annotations module together with tests and docker envs

The purpose of new module is to provide high-level functions for
reading CCL annotations and provide easy way to get them based
on various needs.

Scope of changes:
- implement annotations module (annotations.py)
- provide test data and implement tests (test_annotations.py)
- prepare Makefile as make can serve as unified dev / test / ci environment
  (tox is not an option as does not handle OS dependencies (or I don't
  know it)
- change .gitlab-ci.yml to use make and images defined in this repo
- provide examples of usage in README