DATACMNS-447 - Soften too strict strickt-check in MappingContext.

Previously we directly threw a MappingException in MappingContext.getPersistentEntity(TypeInformation) when the MappingContext was in strict mode and we were given a TypeInformation for which we didn't have a PersistentEntity already.

We now first check whether we should actually create a PersistentEntity for the given TypeInformation if no PersistentEntity is available, before throwing a  MappingException - if we should not then we simply return null (e.g. for simple types like Integer or Double).

Original pull requests: #66, #71.