Field collection support

It seems that some work was done in #1973770: Integration with users, entityreference, taxonomy term references, field collections and nodequeue items and committed a few months ago, but it still doesn't work :(

For example, the code depends on setting the variable uuid_features_entity_field_collection_item, and I can't see any place in the code where this value can be changed.

Attached patch adds "field collection" to feature creation screen and makes some progress, but it's still not working well for me (I have a complex structure of field_collection embedding another field_collection embedding term_reference...)

Field collection support was added in #1973770 but I'm having issues with it adding extra escape sequences to the exported feature. I haven't been able to track down where the issue originates.

Here is an example:

  $field_collections = array();

  $field_collections[] = array(
    'field_name' => 'field_gallery',
    'default_revision' => 1,
    'archived' => 0,
    'uuid' => '056889f9-baa9-43e8-befa-930b1b6505ff',
    'field_image' => array(
      'und' => array(
        0 => array(
          'uid' => 1,
          'filename' => 'gallery-3.jpg',
          'uri' => 'public:\\/\\/masonry-gallery\\/image\\/gallery-3_0.jpg',
          'filemime' => 'image\\/jpeg',
          'filesize' => 166659,
          'status' => 1,
          'uuid' => '1338d34c-104f-4d6f-9255-ff11eb02adda',
          'alt' => '',
          'title' => '',
          'width' => 400,
          'height' => 268,
          'uuid_features_file_data' => '[redacted because this is a huge base64 encoded image]',
        ),
      ),
    ),
    'field_youtube_video_id' => array(),
  );

You can see that the uri is messed up and where I redacted the uuid_features_file_data, that also contained a bunch of weird double backslash escaped slashes.

To fix the issue I added:

$code = str_replace('\\\\/', '/', $code);

right before the export function returns in order to remove all the extra slashes. This fixed it and now I can import and export field collections. :)

Attached is my patch.

Here is another patch rolled with --no-prefix --relative for drush make.