add overlapping dna_align_feature labels to genes

[ajo2995]

When dumping genes, also pull in the names of features from the dna_align_feature table that overlap with the gene. Put these ids into a new field called overlapping_features which is a list of {hit_name: "dna_align_feature.hit_name", analysis: "analysis_description.display_label"}

This is required for the maize v4 search because some v3 gene models may not get into the id history but overlap with new gene models.

Alternatively, we may want to dump dna_align_feature entries into a separate collection which can populate suggestions that lead to region queries.

[ajo2995]

I don't know if it is possible with the ebisearch api, but if an old model doesn't overlap with a new model, it would be nice if the search response could just provide the link to the region where the old model now maps.

This doesn't seem like it would work. I think the links here are generated in the local ensembl server
http://ensembl.gramene.org/Multi/Search/Results?species=all;idx=;q=pad4;site=ensemblunit

[ajo2995]

normally this kind of thing should be taken care of by the xref pipeline, so this feature can be a one-off for the maize v4 search db