userman view.Login: fix css url to relative for `nw`

css stuff is loaded relatively from app.htm via 'file' proto
when css will be loaded from http, this may require changes
auth: "/login" full

authentication process (login):
  first ever '/login' checks for session
  if there is one, then return info for current session in UI
  else if valid user, return available roles

* userman back:
  - provide && load SHA1 hasher
  - `req.session.can` is authenticated flag, not `user`
  - `req.session.user` has copy of id, name, roles User data
  - fix status code on any error
* l10n.um.loginCurrentSession: log in session button text
* model.User: require SHA1, subj, preliminary `User.can()`
* view.Login: width += 10px, clear callback options after FX call
* users db: sha1 password

* waitEvents: occasionally got here
backendEvents: move from ctl.Main to ctl.Userman
model.userman.User: fill model with auth data
auth: '/logout' via `triggerfield` in `view.Login`

When there is active session for typed user,
`view.Login` is filled with that info and button
shows `l10n.um.loginCurrentSession`

To logout and reset view.Login, `triggerfield` can be pressed