[HR] clean model in a changes the hr_applicant model in add the _content...

..._serach method and hr_contract models in add the xml id on the serach and remove _resolve_department_id_from_context method in hr_recruitment model.and add a method _broadcast_welcome hr_recuriemnt model.

- Task: https://www.odoo.com/web#id=8871&view_type=form&model=project.task&menu_id=3942&action=327
- Pad: https://pad.odoo.com/p/r.f9a1kXos2Rn0aS5d
@tde-banana-odoo 
I have tested it and its works fine for me.
check this generated sql:`SELECT "hr_applicant".id FROM "ir_attachment" as "hr_applicant__attachment_ids","hr_applicant" WHERE ("hr_applicant"."id"="hr_applicant__attachment_ids"."res_id") AND (("hr_applicant"."active" = true)  AND  (("hr_applicant__attachment_ids"."res_model" = 'hr.applicant')  AND  ("hr_applicant__attachment_ids"."index_content"::text ilike '%abc%'))) ORDER BY "hr_applicant"."priority" desc,"hr_applicant"."id" desc  limit 80`