add uri fetcher to fetch corresponding files

we can either fetch them to memory or directly
to the harddrive.
extract_class_names is obsolete

hierarchical_class_names should be used instead. one test still fails.
related to #249
should fix new error in #249
Showing related categories
small design refactorings
Corrected english language.
Merge branch 'staging' into 398-delete_ontology_button

Conflicts:
	app/views/ontologies/_menu.html.haml
Some improvements to categories:

* Selected categories are checked in ontologies#edit.
* Show users ontologies on the right in categories#show.
* Refactoring.
Merge branch 'staging' into 714-fix_category_allocation
Merge branch 'staging' into 249-entity_tree
Converted categories JavaScript file to CoffeeScript.
fast fixing the problem with explicit thing subclass sentences

its a fast fix for 249 till the tarjan algorythm is
implemented
use uri-fetcher for the external repository.
Merge branch 'staging' into 633-fix_download_of_external_files
fix ontology button display permission check
fix namespacing and method-name for uri-fetcher.
fix module inclusion and param for downloading.
adjust external-repository fileadd for location.
move filedownload for external repository

The file download step for the external repository
needs to be moved into the 'reference' node proc,
in order to handle its location attribute.
Test ability on repository, not parent (distributed) ontology.