Return stewardship w/ default mobile fields and search fields

Because this is adding a new type of field group that the mobile do not
have the ability to render yet, these changes are only available in v3 of
the API.

This is intended to be the final feature in v3, and all new breaking
changes should be part of v4.
Using ``DEFAULT_MOBILE_API_FIELDS`` is a good idea. We should try and move what we need to move to make that happen.

We don't want to tie our hands if a customer wants to add a collection UDF, but not expose it on the mobile app (maybe because it is 7 fields wide and is used by admins only for internal reporting). That is definitely an edge case, but the more that we backtrack on making things configurable by instance, the more freedom we steal from ourselves to quickly (read: cheaply) meet the wacky needs of potentially high paying customers.