add CHANGELOG.md to template and update metadata

[jimustafa]

Added CHANGELOG.md to the template and an associated entry in project.urls. Also updated the label for the link to the issue tracker to be consistent with what is given on packaging.python.org.

Referencing pypa/packaging.python.org#1183 here as there should be some coordination between packaging.python.org and sampleproject to maintain consistency in how the metadata is presented.