Add DIMP case study metadata type

Add DIMP case study
Make Model editor work for models, model applications and case studies.

## Linking between datasets and models
Created a more general way of linking between document types

There is  a Relationships set in MetadataDocument that can hold any relationship between documents, it just holds the name of the relationship and the target of that relationship. 

It is being used for relationships between models, case studies and datasets in DIMP but can be expanded to the other linking requirements in time.

## Problems with post processing
Started moving away from post processing documents as there are problems with attribute duplication with the post processing approach. An example is the parentIdentifier, deleting the parentIdentifier did not delete the parent attribute so a document continued to appear as a member of  a Series

Now when rendering a template information is looked up from the JenaLookupService, essentially an identifier is converted into the presentation ready information but not stored on the document.

I have not removed all the post processing code, but will be removing  as needed. 

@jcoop

See merge request !19