reorganize cukes into desktop and mobile folders

features/desktop/accepts_invitation.feature

features/desktop/activity_stream.feature

features/desktop/aspect_navigation.feature

features/desktop/blocks_user.feature

features/desktop/change_email.feature

features/desktop/change_password.feature

features/desktop/closes_account.feature

features/desktop/comments.feature

features/desktop/connects_users.feature

features/desktop/contacts.feature

features/desktop/conversations.feature

features/desktop/donations.feature

features/desktop/download_photos.feature

features/desktop/edits_profile.feature

features/desktop/follows_tags.feature

features/desktop/hovercards.feature

features/desktop/invitations.feature

features/desktop/keyboard_navigation.feature

features/desktop/logged_out_browsing.feature

features/desktop/logs_in_and_out.feature