Address feedback

app/controllers/projects/application_controller.rb

app/controllers/projects/uploads_controller.rb

app/finders/issuable_finder.rb

app/finders/joined_groups_finder.rb

app/helpers/visibility_level_helper.rb

app/models/ability.rb

app/models/group.rb

app/services/groups/create_service.rb

app/services/groups/update_service.rb

app/views/groups/show.html.haml

app/views/projects/_home_panel.html.haml

app/views/shared/groups/_group.html.haml

app/views/shared/projects/_project.html.haml

db/migrate/20160301124843_add_visibility_level_to_groups.rb

...3_add_default_group_visibility_to_application_settings.rb

db/schema.rb

spec/features/security/group/internal_access_spec.rb

spec/features/security/group/private_access_spec.rb

spec/features/security/group/public_access_spec.rb

spec/finders/joined_groups_finder_spec.rb