Orphan osra num

JIRA story https://osraav.atlassian.net/browse/OSRA-77

- Add sequential_id & osra_num columns to orphans table
- Create associations Partner - OrphanLists - Orphan
- Create Orphan#generate_osra_num
- Add osra_num fields to orphan index, show & edit (field disabled)
- Improve spec coverage for the Orphan model

### JIRA
OSRA-77 #Code-Review
OSRA-78 #Code-Review
OSRA-79 #Code-Review
OSRA-80 #Code-Review
OSRA-81 #Code-Review
OSRA-154 #Code-Review
OSRA-156 #Code-Review