[IMP]hr_recruitment :Add a stat button of created employee

- Task: https://www.odoo.com/web#id=10240&view_type=form&model=project.task&menu_id=3942&action=327
- Pad: https://pad.odoo.com/p/r.xqYlcou3kRcM4hhF
Simply test if applicant is not null, and if it has an employee id.