expand relationship mapping on schema to allow nested field filtering

[kiptoomm]

• the current mapping is only limited to a schema's Relationship fields;
  fields that are declared as Nested objects would otherwise be missed
• see issue Support for filtering on nested fields #155 for details

[coveralls]

Coverage remained the same at 95.057% when pulling a47af3b on kiptoomm:develop_filter_nested_field into 31d0018 on miLibris:develop.

[coveralls]

Coverage remained the same at 95.057% when pulling a47af3b on kiptoomm:develop_filter_nested_field into 31d0018 on miLibris:develop.

[coveralls]

Coverage remained the same at 95.057% when pulling a47af3b on kiptoomm:develop_filter_nested_field into 31d0018 on miLibris:develop.

[kiptoomm]

closing because the base branch develop is too far behind master