Fix #174 Add properties field to Entity concept

I also don't think we need the sentence after this:
> Moreover, for each property it contains a set of associated property values, possibly empty.

draft/index.html

@@ -270,8 +270,9 @@ <h3 data-link-for="entities">Entities</h3>
              <dd>an optional <emph>description</emph> as a human-readable string;</dd>
              <dt><code>type</code></dt>
              <dd>an array of <a>types</a>, possibly empty;</dd>
+             <dt><code>properties</code></dt>
+             <dd>an array of <a>property</a> fields and associated <a>property values</a> for the entity, possibly empty;</dd>
            </dl>
-           Moreover, for each <a>property</a> it contains a set of associated <a>property values</a>, possibly empty.
         </p>
         <p>
            Reconciliation services MUST define in their <a>service manifest</a> a <dfn>URI template</dfn> for entities,