O294 sponsorship end date validation

https://osraav.atlassian.net/browse/OSRA-294
This is connected to:  https://osraav.atlassian.net/browse/OSRA-298

Sponsorship model validatation for end_date
- can't be before start date
- can't be blank

plus rspec and cucumber tests

Andrey and me worked on this.
I am guessing this has been changed because you want a return status rather than an error being raised ?
if so you could keep the conciseness of the original statement with something along the lines of 
```
updated = update_attributes(active: false, end_date: end_date)
set_orphan_status_to_previously_sponsored if updated
updated
```
I think this makes the purpose / intent of the method more obvious