Create skeleton for managemetadata + constructor
Merge branch 'feature/ximdex-metadata' of github.com:XIMDEX/ximdex into feature/ximdex-metadata

* 'feature/ximdex-metadata' of github.com:XIMDEX/ximdex: (23 commits)
  Some improvements on RNG schemes for metadata: deny deletion and change its name and by default, set its type to metadata RNG schema.
  Minor changes on Xtags template and action.
  Adding correct type tag when creating a new tag - OntologyBrowser
  Changing button for anchor in main-action - OntologyBrowser
  Minor issue
  Puts back to suggested tags list the tags being removed from selected list
  Adding multi-tab functionality in OntologyBrowser
  Showing elements in OntologyBrowser widget with no childrens
  Fixes document tag list cannot be persisted with no tags
  Fixes new tags to be added in other tab taglist when there are more than one tags tab opened
  Fixes tags input widget to be instantiate twice in the same action
  Adding selectors to navigate over schema.org taxonomies
  Adding full schema.org ontology
  Fixing comments
  Recovered RelTagsDescriptions files
  Adding support to hidden nodes
  New entry on Namespaces table for the OntologyBrowser
  Deleting some unuseful classes for ximTAGS module.
  Updating getSectionPath
  Supporting rdf as default extension like xml
  ...