[BugFix] Fix OECD Unemployment Age Brackets & Fix No module named 'pkg_resources'

[deeleeramone]

1. Why?:

   • The age brackets have changed on OECD Data Explorer and there are only 3 valid brackets.
   • pkg_resources is deprecated, and version needed to be updated to use importlib.metadata.
     • This caused an ImportError and the Platform failed to initialize when 3.9 was used.

In other versions I receive a warning:

DeprecationWarning: pkg_resources is deprecated as an API. See https://setuptools.pypa.io/en/latest/pkg_resources.html
  import pkg_resources

2. What?:

   • Update the choices for Age in economy.unemployment
   • Refactor version.py to use importlib.metadata
   • Update static assets.

3. Impact:

   • Age brackets working as expected.
   • Python 3.9 will now import the Platform.