[ADD] cleaned up, prepare for OCA PR
[ADD] some comments
[FIX] pep8
[FIX] license and updated module description.
Add 'hr_roster/' from commit 'ea652a145a42a49da3253eab914e5f2be7b2cf34'

git-subtree-dir: hr_roster
git-subtree-mainline: d8ab40393123d62cd073ae414dcbe72e0a42aaf0
git-subtree-split: ea652a145a42a49da3253eab914e5f2be7b2cf34