Edit Leave application + validation for leave + specs

1) Admin can edit leave
2) Employee can edit only own leave only if it is pending
3) Casual leave can't be more than 2 days
4) If sick leave is more than 3 -> Show notification to submit medical
certificate
Merge branch 'leave_application' of github.com:anujaware/intranet into leave_application
Send approval mail if leave updated and pending