Add version-specific handling to the refactored tools

[nicoweidner]

The improved structure on https://github.com/spdx/tools-python/tree/refactor-python-tools should make it easy to add version-specific handling to the Python tools. A version parameter should be added to the CLI tools, which will then be passed along whenever relevant. In the case of 2.2 vs 2.3, only the validation layer should require some version-specific logic, while 3.0 is expected to be a completely separate logical branch because of the massive changes when compare to 2.x.