MBS-2417: Allow loading relationship type documentation
Add updatable documentation
Merge documentation setting/updating into insert and update subroutines
Allow setting relationship documentation in the AddLinkType edit
Allow editing the documentation string for relationship types via the EditLinkType edit
Allow editing documentation via the website and display documentation changes in edit history
Display further documentation for relationship types

Adds a link to the create/edit relationship pages, which links to
further documentation for relationship types. Currently this page shows
the relationship name, description, and any further documentation.
Merge branch 'mbs-5772'

* mbs-5772:
  Display further documentation for relationship types
  Allow editing documentation via the website and display documentation changes in edit history
  Allow editing the documentation string for relationship types via the EditLinkType edit
  Allow setting relationship documentation in the AddLinkType edit
  Merge documentation setting/updating into insert and update subroutines
  Add updatable documentation
  MBS-2417: Allow loading relationship type documentation

Conflicts:
	lib/MusicBrainz/Server/Controller/Relationship/LinkType.pm
	lib/MusicBrainz/Server/Edit/Relationship/AddLinkType.pm
	lib/MusicBrainz/Server/Form/Admin/LinkType.pm
	root/edit/details/add_relationship_type.tt
	script/create_test_db.sh