simplify: use only one controller for the one group archive

app/controllers/group/archive_controller.rb

app/controllers/group/archives_controller.rb

app/helpers/group/links_helper.rb

app/jobs/group_archive_job.rb

app/models/group/archive.rb

app/views/group/archive/_page.html.haml

app/views/group/archive/indexpage.html.haml

app/views/group/archive/page.html.haml

app/views/group/archive/show.html.haml

app/views/group/archive/singlepage.html.haml

config/locales/en/groups.yml

config/routes.rb

extensions/themes/default/navigation.rb

test/functional/group/archive_controller_test.rb

test/functional/group/archives_controller_test.rb

test/integration/group_archive_test.rb