Fix searching organisations by name (closes #88)

When searching organisations by name, use both the
http://www.w3.org/2004/02/skos/core#prefLabel and the
http://xmlns.com/foaf/0.1/name fields.
Use `Operator.AND` for organisation-by-name queries (see #88)
Set up ngram analyzer for the http://xmlns.com/foaf/0.1/name field
Use id_analyzer on http://purl.org/dc/terms/identifier (closes #92)
Merge pull request #91 from fsteeg/org-by-name

Fix searching organisations by name and ID