Variable for defining whether the project will have a release cycle

[nekeal]

• Replace license badge from pypi to github
• Replace pypi python version badge with a static one
• Add new releasable variable. When false, some parts of the template regarding making a release are not included.

Mai goal of this pull reuqest is to be able to use this template for a python project that does not need to be released to PyPI. When releasable variable will be set to False:

• some sections of a README will not be included
• python-kacl package won't be installed
• Some file regarding releases such as changelog or workflows will be added to .gitignore.