Added the option to define the ldp:insertedContentRelation that the IndirectContainer will use

See section 5.5.1.2.
IndirectContainers use the property ldp:insertedContentRelation to specify the indirection. The current implementation didn't specified this property on the resource it was posting, so it was failing as a Bad Request.

A new option was added to the main .xml file. It is optional because it was also included a default one, foaf:primaryTopic, which will be used if the option is not specified.