modify old rake task for new tree mechanism
adding migration for cleanup

to remove all old version edges there is an migration
adding task for generating tree of specific ontology

to build the tree manually for one specific ontology
there is now an rake task to do this
changes according to pull request
Merge branch 'staging' into 819-adjust_entity_tree_rake_task
Merge pull request #883 from ontohub/819-adjust_entity_tree_rake_task

819 adjust entity tree rake task