TEIIDDES-2207: Correct Web Service issue when view lacks a primary key

* When a view model lacks a primary key, the model lacks an input element

* WebServiceBuilderHelper
 * Refactor the SQL generation function to only create declarations and
   assignment if the model has any input elements.
 * Removes default 'example' SQL since this is not valid and likely to
   provide nothing but confusion to users

* SQLStringVisitor
 * Avoids possible NPE when the object list is null