Change imports to use absolute paths

This is both in an effort to get tox fully functional for
all tests in the project, and also to better follow the
OpenStack style guidelines (http://docs.openstack.org/developer/hacking/#imports)
which says that relative imports should not be used.

Since aboslute imports are used, running "python main.py" will no longer
work. Now you must use "python -m translator.main" from the project root.