Identical ContentTitleText should trigger hint

[wolfgangw]

Given a DCP with more than 1 CPL: dcp_inspect should generate a hint when there are identical ContentTitleText strings across those CPLs.

Having identical ContentTitleText strings across multiple CPLs is not an error as per specification – the DCNC is not specification but rather a recommended nomenclature – but it does point strongly to an authoring issue. The hint would clearly be helpful.