Feeds entity reference

Adds new items for feed processor mapping:

1. Referencing and referenced entities (for the feed node which can contain feed URL value) as the sources.
2. Entity reference fields as the targets (it can be set to any value, not just to imported nodes, as Entity reference module does).

The possible use case:

Cities have news associated with them (by using entity reference field in the news content type). Any city can have some external RSS feeds which are to be imported with news creation, and the created news must have the city reference field set to the proper city.

Using this module, you can solve the problem easily. Just create new content type which will serve as feed node for configuring RSS URL and add entity reference field from city content type to this feed node type. After that, create new feed importer and in its mapping configuration, add the mapping from the field which contains city to feed node reference to the field which contains news to city reference.

Future development:

1. Add Organic groups support (special query for referencing entities is needed).
2. Add referencing or referenced entity fields as mapping sources.