avoid indexing "email" field type in Solr

[pdurbin]

The email field type was added in #494 but we want to special case indexing of it.

[pdurbin]

In general our mantra has been "make all dataset fields searchable" but we are deciding against this for the "email" field type since we don't want to risk exposing email addresses.

Now "email" field types such as distributorContact are no longer indexed into Solr. Passing to QA. Please note that you can use scripts/search/query to query Solr directly. Also, in order remove email addresses for existing datasets from Solr, you'll need to run "index all".

I didn't actually remove from schema.xml because we'll be updating it soon enough for #754 . Also, it's not clear from #747 if "the list of potential collaborators should be searchable" means a Solr or database search.

[kcondon]

Confirmed, both author contact email and distributor contact are not longer searchable after index all.