Allow groups to appear in the search results if the group owner allows it

CHANGELOG

app/controllers/groups_controller.rb

app/finders/groups_finder.rb

app/helpers/search_helper.rb

app/models/group.rb

app/views/groups/edit.html.haml

db/migrate/20151103001141_add_public_to_group.rb

db/schema.rb

spec/finders/group_finder_spec.rb

spec/helpers/search_helper_spec.rb

spec/models/group_spec.rb