Sponsor affiliate validations

OSRA-209 https://osraav.atlassian.net/browse/OSRA-209
SponsorType must match affiliate type

- validate that sponsor_type matches affiliate on sponsor creation
- make sponsor_type, branch & organization readonly in sponsor
- disable selectors for Sponsor Type, Branch & Organization on the Sponsor Edit page

- update seeds, specs & features to conform to the new validation
I don't see how in this case. The use of `attr_readonly` captures the intent and encapsulates the required functionality very well - these attributes can be written on create, but for a persisted object can only be read.
Whitelisting would have to be done in the controller on a per-action basis since we still want these attributes to be writable on create.