Add cross reference between Applicant and Employee

To represent hirings
Filter hired applicants in applicants indexes
Rename Hired as IsHired
Allow to filter applicants by hiring status

(Application Level)
Refactor SearchApplicant

To move logic together with parameter definition
Allow to filter applicants by hiring status

(UI Level)
Hire Applicant logic
Hire Applicant UI
Show related employee link in hired applicants
Show employee related applicant (if exists)
Merge pull request #271 from andresmoschini/applicant-to-employee

Applicant to employee