hrjob: Add notice period fields

Add two-part field with values like "3 weeks", "2 months", "1 year"

• Update DB (table: civicrm_hrjob)
• Update "View Contact -> Jobs -> General" UI (Note: Certainly requires updates to hrjob-general-template. It's possible but much less likely that it would need updates to model [CRM.HRApp.Entities.HRJobP], controller [CRM.HRApp.General.Controller], or view [CRM.HRApp.General.View] in js/entities/hrjob.js, js/general/edit_controller.js, or js/general/edit_views.js.)

FWIW, there's a similar two-part field in the "Hours" screen (hours_amount/hours_unit).

When generating the dropdowns, there's some ugliness. CRM_HRJob_Page_JobsTab::getFieldOptions() has a hard-coded list of fields/lists which should be available. It would be much cleaner if getFieldOptions() simply exported all option-lists for all dropdown fields in the HR entities.