fix(console): a console that cannot open says why and starts no client

A stopped VM, an unreachable or unsupported console and a disabled serial
console rendered the lite VNC page under the error: it connected to novncd
anyway, showed "Something went wrong" and offered keys, Scale and Send
CtrlAltDel for a console that was not there. A refused console was a bare
text 403 inside the popup.

- console-error.html: the console shell with the VM's name and the reason,
  no menu and no script; a refused or unknown VM gets it with 403 and
  without the VM's name, as before for everyone (no superuser exception).
- The view signs the console token only for a page that connects.
- console-menu.html: the Send key(s) menu and Fullscreen, included by the
  console pages; the serial page lists only the keys it sends (the VNC
  groups did nothing there).
- Every console window is titled "<VM> - Console".
- The lite page no longer takes a VNC password from its link.
- The shell lost its 850px x 600px corner radius (a grey arc on the
  serial and error pages) and spans the window (container-fluid).

console/templates/console-error.html

@@ -0,0 +1,7 @@
+{% extends "console-base.html" %}
+{# a console that cannot open: why, and no console client #}
+{% block navbar %}{% endblock %}
+
+{% block content %}
+<div class="alert alert-danger rounded-0 m-0" role="alert">{{ console_error }}</div>
+{% endblock %}