Refactor version into setup.py

Remove requirement to import pymessagefocus in the setup file as this in turn attempts to import an external dependency six which means the install will fail in a clean environment.
Remove version file entirely, all it's contents merged into setup.py

Relates to internal TMS case 5974
Merge pull request #1 from TriggeredMessaging/unable-to-install-package

Refactor version into setup.py