add homebrew installed hets to search_path.
bump minimal hets working version number

Importing referenced OWL-ontologies will fail for
earlier versions.
Merge pull request #578 from ontohub/os_x_hets_management

OS X hets management
optimize team_permissions query by using pluck

pluck allows us to extract fields directly from
a query without the need to instantiate model
objects (very expensive).
add spec to find the highest permission.
add methods to retrieve highest permission

- and use it for ssh-push access determination
- makes tests green.
Merge branch '599-fix_group_permissions_for_ssh' into develop