feat(networks): the network pages on Bootstrap's cards, tables and dialogs

As the storage pages; reviewed with Codex.

- The list is a card per network: its name with Active or Stopped and
  Autostart badges, its type (network_mode: Isolated, NAT, Routed,
  Open, Bridge, Macvtap, SR-IOV), its device, and each address with
  its DHCP range; a bridge or macvtap network's addresses come from
  the outside network.
- A network's page: its heading starts or stops it, the menu sets
  autostart and deletes a stopped one. A Network card tells its state,
  type, bridge or interface, MAC and what the type does; a card per
  address (every <ip>, each with its DHCP range dialog, which libvirt
  takes on a stopped network); its fixed addresses of every subnet in
  one table, searched, each with Edit and Delete, one dialog adding
  and editing them; the VMs whose definition names it, connected or
  configured, linked (wvmNetwork.get_vms, one domain listing, a VM
  undefined meanwhile left out); its
  bandwidth limits where libvirt sets them (not on macvtap or SR-IOV
  networks), in KiB/s, from the saved definition with a note that a
  running network takes them when restarted; its XML in an accordion.
  The page reads the running and the saved definition once each, and
  only to render itself: its actions, which all redirect, read nothing
  of it first.
- The New network dialog is one form, as the New pool one: the type
  as radio cards (the radio_card.html include, now shared by both),
  the chosen type's fields only, IPv6 with its box, a bridge or
  interface suggested from the host's (get_host_interfaces, not the
  bridges libvirt made for its own networks); a refused network or
  one libvirt refuses opens the dialog again with what was entered,
  the reasons beside the fields and focus on the first.
- What the New pool and New network dialogs share is one script,
  static/js/choice_dialog.js: the radio cards show their fieldsets
  (data-kinds) and a refused form opens again focused on its first
  refused field; each dialog keeps only its own changes.
- The fixed-address dialogs per family go to the page's own dialog.

static/js/choice_dialog.js

@@ -0,0 +1,38 @@
+// A create dialog of one form whose radio cards choose what is made (the
+// New pool and New network dialogs): a fieldset shows for the choices in
+// its data-kinds, the others are hidden and disabled, so neither checked
+// nor sent; onChoose(value) does what else a choice changes. A form the
+// server refused (data-open on the dialog) opens again with what was
+// entered: the choice sent back, or the first when it is offered no more,
+// and focus on the first refused field shown, or on the reasons.
+function choiceDialog(dialog, radioName, onChoose) {
+    var form = dialog.querySelector("form");
+    var radios = form.querySelectorAll("input[name=" + radioName + "]");
+    function choose(value) {
+        form.querySelectorAll("fieldset[data-kinds]").forEach(function (fields) {
+            fields.hidden = fields.disabled = !fields.dataset.kinds.split(" ").includes(value);
+        });
+        onChoose(value);
+    }
+    radios.forEach(function (radio) {
+        radio.addEventListener("change", function () { choose(radio.value); });
+    });
+    var chosen = form.querySelector("input[name=" + radioName + "]:checked") || radios[0];
+    chosen.checked = true;
+    choose(chosen.value);
+    if (dialog.hasAttribute("data-open")) {
+        dialog.addEventListener("shown.bs.modal", function () {
+            var refused = Array.from(form.querySelectorAll("[aria-invalid=true]")).find(function (field) {
+                return !field.closest("fieldset[hidden]");
+            });
+            var reasons = form.querySelector(".form-errors");
+            if (refused) {
+                refused.focus();
+            } else if (reasons) {
+                reasons.tabIndex = -1;
+                reasons.focus();
+            }
+        }, {once: true});
+        bootstrap.Modal.getOrCreateInstance(dialog).show();
+    }
+}