Tags: retrieve tags assigned to Title record

Tags should be returned by any variation of mod-kb-ebsco API GET method which retrieves Title record. There is no need at the moment to return tags for title collection.
Affected API methods:

• GET /eholdings/titles/<titleId>

Tags should be placed inside record's attributes as a separate object with name "tags"

Tag object schema is common for all records and can be found in /raml-util/schemas/tags.schema

To support tags retrieval mod-kb-ebsco has to provide a storage there tags are represented as plain values (simple string like "important", "urgent", "spitfire") linked to associated records. The linked record should be represented by record id and record type. Example for a title:

• record id = 11564526;
• record type = "title"

Record type is required to avoid possible collisions between ids of records of different types.