[api][backend] move some more configurations from options.yml and BSConfig.pm into /configuration api.

values in options.yml are still read and used. But they are not changable via
/configuration api and should be remove therefore.

This includes

 - anonymous ( was allow_anonymous )
 - registration ( was new_user_registration )
 - default_access_disabled ( was default_access_disabled )
 - allow_user_to_create_home_project ( was allow_user_to_create_home_project )
 - disallow_group_creation ( was disallow_group_creation_with_api )
 - change_password ( was change_passwd )
 - hide_private_options ( was hide_private_options )
 - gravatar ( was use_gravatar )
 - download_url ( was download_url )
 - ymp_url ( was ymp_url )
 - errbit_url ( was errbit_host )
 - bugzilla_url ( was bugzilla_host )
 - http_proxy ( was http_proxy )
 - theme ( was theme )
 - download_on_demand (from BSConfig.pm)
 - project_key_generation (from BSConfig.pm)
 - multiaction_notify_support (was multiaction_notify_support)
[api] fix rollback of OBS:Issue addition