This dramatically speeds up rendering with many translators.

.hidden is a default class in tailwind.

We're not using it, so its just confusing.

This is more consistent and actually removes the elements from the layout.

The commit also hides the conditional elements by default, which should
be a more natural loading experience.

This allows signup, profile edits and login/logout.
Note that due to poor naming, there are conflicts between our session
model und what devise thinks a session should be. In particular, we have
to rename `new_session_path(resource_name)` -> `new_user_session_path`
and `session_path(resource_name)` -> `user_session_path`.

Cf. https://github.com/heartcombo/devise/issues/2800

This is just to preserve history. These are unmodified copies generated
by `rails generate devise:views`.

The state is now fully client-side and handled in session_controller.
This allows us to continue to broadcast the session frame to everyone.

Cf. https://github.com/pretalx/pretalx/issues/1910

- Add X button to clear filter
- Restrict maximum height
- Visually group list with filter input