Show orphans sponsorship status

https://osraav.atlassian.net/browse/OSRA-177

- add fields for sponsorship status & current sponsor (if present) to orphan show view
- add disabled sponsorship status field to orphan edit view
- create 2 new sponsorship-related methods in the Orphan model
- make step definition for 'Unable to change field' more versatile at the cost of complexity & brittleness - worth it?

OSRA-177 #Code-Review
I wasn't arguing in for longer `if`s, just about the use of `if` in views. If something can be shortened without losing clarity - as in all cases in this PR - I'm fully in favour. So, refactoring is in progress.