Abilities extended. Resources security improved

app/controllers/application_controller.rb

app/controllers/commits_controller.rb

app/controllers/issues_controller.rb

app/controllers/merge_requests_controller.rb

app/controllers/refs_controller.rb

app/controllers/repositories_controller.rb

app/controllers/snippets_controller.rb

app/controllers/wikis_controller.rb

app/models/ability.rb

app/models/project.rb

app/views/help/permissions.html.haml

app/views/issues/_show.html.haml

app/views/layouts/_project_menu.html.haml

app/views/merge_requests/show.html.haml

app/views/widgets/_project_member.html.haml

app/views/wikis/show.html.haml