Add resource field filters for filtering and object creation

Implemented a way for resources to be filtered by a field setting and new objects to also use that same setting. The primary use case is to scope objects by the user_id who owns them. The resource fields can now be configured so that all calls to GET will apply this filter, calls to POST will use this filter for the specified field, and POST/PUT cannot modify this field. This is implemented with modifications to the Field class and also renaming Fetcher to Adapter because it now also creates objects.