(Improvement) Support include and search field params

[stevelacey]

Include fields

Include fields is a dict of fields to include when ?include=skills,team is passed.

The dict should be keyed by field names, and the values are passed through to either
prefetch_related or select_related.

class ProfileList(CreateAPI, ListAPI):
    model = Profile
    include_fields = {
        "skills": Prefetch("skills"),
        "team": "team",
    }

Search fields

Search fields is a list of fields that are used for icontains lookups via ?q=.

The ?search=id,name query param can be used to filter search_fields.