Merge pull request #541 from ontohub/534-fix_alternative_iri_varchar_issue

switch iri column of AlternativeIri to text
Better description of repository cloning methods in view.
Merge pull request #542 from ontohub/536-explain_clone_with_ssh_git

Better description of repository cloning methods in view. Fixes #536.
Updated Ruby version to 2.1.0.
introduce hierarchical class-extraction method.
actually use entities for categorify.
fixing minor error in the related ontologies
showing numbers on the categories search tree
Updated some gems.
Merge branch 'staging' into 476-number_of_ontologies_in_category_on_categories_index
Merge pull request #544 from ontohub/476-number_of_ontologies_in_category_on_categories_index

Number of ontologies in category on categories index.
Show repositories and ontologies and landing page again.
possible values for metadata
Task description type text, metadata in seeds.
Merge pull request #546 from ontohub/538-correct-seeds-for-formality-level-etc

Possible values for metadata.
Repaired task unit test.
More gem updates.
Some improvements regarding to categories import.
Instructions added for installing a recent version von Redis.
Change the icon of Ontohub to the one of OOR