Close issue #105, Tie smart links setups to document types
Remove unused class
Add ModelAttribute helper class to document the attributes of a document available for user interaction
Add document label field help_text
Document the usable document attributes added by the metadata app using ModelAttribute class, add DocumentMetadataHelper to help retrieve a document metadata value easier
Update the document linking form to show the available mode attributes
Remove usage od MetadataClass and simplify smartlink query building
Expand the size of the foreign_document_data field
Show the available document attributes during document indexing setup form
Remove usage of the MetadataClass during index calculation code
Add the comments related field to the document attributes documentation
Update the document index documentation figures to reflect the usage changes
Add label to the registered Document model fields
Hide DocumentSerializer import