Modified `pyproject.toml` to update project name, URLs and version.

Changed `cookiecutter.json` to incorporate additional variables, which
include breaking `project_name` into three variables (`project_name` as
a title, `repo_name` for the repository and `package_name` for the
Python package), `scm_platform` for choosing between GitLab and GitHub,
`scm_username` replacing `github_name`, others for defining use of
testing, formatter, docstring style and options for creating Dockerfile,
AUTHORS.md and documentation structure.

Renamed cookicutter reference for repository name in order to use the
newly created `repo_name` variable.

Removed the project's GitHub structure and replaced with GitLab
templates instead.

Restructured GitHub templates under a `_templates` folder to also
include GitLab templates, starting with Issue and Merge Request
templates.

Added AGPL, LGPL and Mozilla licences as options.

Updated CODE OF CONDUCT to Contributor Covenant v2.1 in both proje...