Add field to DataField and DataConcept for excluding from search index

Fix #172.

Signed-off-by: Don Naegely <naegelyd@gmail.com>
Likewise, this does not exclude the concept, but the fields that are associated with this concept. I presume the idea for having this on the concept as well are for the cases when the underlying field(s) have nothing to do with the concept. For example, a diagnosis summary concept that uses a patient ID internally for the lookup. Is that what you were thinking as well?