Add a dedicated pkgdb2version file that contains only the version information
Let pkgdb2client rely on pkgdb2version to set its version information
Update the setup.py to rely on pkgdb2version to set its version

Fixes https://github.com/fedora-infra/packagedb-cli/issues/6
Fix the test and expand them to test get_package for multiple branches
Add a global boolean allowing to turn on/off the authenticated tests (saves time)
Remove un-used lines of code
Small pep8 clean up