ui: implement OpenId login

ui: implement OpenId login

Signed-off-by: Dietmar Maurer <dietmar@proxmox.com>
 [ Thomas: amended the following changes:
 - factor out openid_login_param to widget-toolkit as
   getOpenIDRedirectionAuthorization and use it
 - use camel case to match our JS style guide and our framework (and
   basically the rest of the JS world)
 - minor cleanups like moving variable definition into the single if
   branch their used
 ]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>