let history recognize file renames as a change
recreate basic diff infrastructure
introduce Commit class for history, lazy computing of deltas
delegate commits to git
Move filepath from ontology to ontology_version
remove debug log
detect moved ontologies, save them properly
fix files controller's ontology query
don't depend on ontology_version_id to be set correctly
further steps to move path into ontology_version
use path in an ontlogy if it has no version
cosmetics
adding cucumber-rails gem
introducing cucumber files
changing the old session_test minitest to cucumber
fix missing versions in factory
add specs for permissions check for git/ssh.
pass specs and add private_* support to git/ssh.
extract permissions-check (git/ssh) into methods

Thise includes the following:
  - Everyone-Case
  - Permission-based handling
  - Role-based handling.
small fix: use each instead of map