Update URL/query used to fetch titles from erm

The current way of retrieving titles from erm is not optimal, as the way its currently implemented in EusageReportsApi.java#L497 is not searching specifically for a resource with an ISSN of 1557-7341 but actually for a resource with an identifier of 1557-7341 where that resource has at least one identifier in the ISSN namespace.
That is - these two criteria would act separately then be combined with AND. This is a subtle difference of course and in most cases will work for ISSN because their format is so specific.

Instead the following contruct should be used:

String uri = "/erm/titles?"
        + "filters=(identifiers.identifier.ns.value%3D%3D" + type
        + "%26%26identifiers.identifier.value%3D%3D" + identifier + ")";

Also:

/erm/titles works exactly the same as /erm/resource but will only search titles (where /erm/resource searches both titles and packages together). The request parameters and response format are exactly the same

Also:

The support for the new grouping syntax in search is only available with 6.0 upwards