GC-45: Update copyright information:

- Changes to code base were previously done in 2020 as well (based on
git history).

Noticket: Fix the release script confirmation verification:

- Conditional for verifying user's request to publish the release was
missing.

GC-24: Added release script:

- Updated package requirements for development to include twine (for
the release process).
- Added initial version of release script. The script takes care of
preparing the local git repository (maintenance branches, tags,
updates to release notes and setup.py), as well as pushing the
changes to both origin git repository and distribution package to
PyPI.
- Switched to using version 0.0.0 as development version.