Code clean up
Added RelationAdder to Repository so the Reletion related methods can be removed.
Make RelationTypes injectable.
Refactored RelationRef so it stores the relation name as well.
Refactored addRelation of DomainEntity, so only the relationRef can be added.
Moved the creation of the regular relation refs to the RelationRefCreator
Ignore the relationName-property when serializing a RelationRef, to maintain the API.
Fixed typo
Made method package private to limit the usage.
Added the posibility to add a RelationType to RelationBuilder.
Refactored addDerivedRelations, so it can use the addRelationMethod of RelationRefCreator.
Start developing version 3.0.0
Use one instance of NoOpIndex in the NoOpIndexFactory.
Update version number of index page
Release 2.6.0
Start developing version 3.0.0
Use one instance of NoOpIndex in the NoOpIndexFactory.
Merge branch 'hotfix-cmdi-generator' into develop

Conflicts:
	pom.xml
	timbuctoo-core/pom.xml
	timbuctoo-instance/pom.xml
	timbuctoo-model/pom.xml
	timbuctoo-rest/pom.xml
	timbuctoo-services/pom.xml
	timbuctoo-solr/pom.xml
	timbuctoo-tools-config-example/pom.xml
	timbuctoo-tools-instance/pom.xml
	timbuctoo-tools/pom.xml
	timbuctoo-vre/pom.xml
	timbuctoo-war-config-example/pom.xml
	timbuctoo-webpages/pom.xml
Generate the right front-end url
bump version