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

As the network and interface pages; plan reviewed with Codex.

- The list is one table with a search: each filter's chain, priority,
  number of rules, the filters it references, and how many VMs and
  filters use it directly; a row's menu clones it (one shared dialog,
  the copy's name filled in) or deletes it, Delete disabled and saying
  so while it is in use. Without the VMs (a host that fails to list
  them) the list is not shown: it would offer to delete filters in use.
- New filter is one dialog with the filter as XML in the Ace editor,
  from a starter filter, with what in, out and priority mean and a link
  to libvirt's format.
- A filter's page: a Filter card (UUID, chain, priority, the VMs that
  use it directly, linked, and the filters that reference it, linked);
  its references with their parameters (one to a filter gone from the
  host marked as missing, not linked), removed per row, added from a
  select of the filters it can reference; its rules with the action as
  a badge, the direction as to or from the VM, the priority (500 where
  none is given), every protocol element with its attributes, a rule
  of no protocol as any traffic of the chain, and when it does not
  track connections; Add rule as an XML dialog; the XML, collapsed,
  saved in place.
- The editors size themselves when shown and keep their label for
  screen readers; tables keep their hidden
  header text inside them, so a phone does not scroll the page
  sideways. add_nwf_rule.html goes (the dialog is on the page).

vrtManager/nwfilters.py

@@ -34,10 +34,12 @@ def filter_info(nwfilter, tree):
 
 class wvmNWFilters(wvmConnect):
     def get_nwfilters_info(self):
-        """Every filter of the host (filter_info) by name: one listing, one XML
-        read per filter."""
+        """Every filter of the host (filter_info), with the filters that
+        reference it, by name: one listing, one XML read per filter."""
         filters = [filter_info(nwfilter, etree.fromstring(nwfilter.XMLDesc(0)))
                    for nwfilter in self.wvm.listAllNWFilters(0)]
+        for nwfilter in filters:
+            nwfilter["referenced_by"] = [other["name"] for other in filters if nwfilter["name"] in other["refs"]]
         return sorted(filters, key=lambda nwfilter: nwfilter["name"])
 
     def get_users(self):
@@ -101,14 +103,14 @@ class wvmNWFilters(wvmConnect):
         self.get_nwfilter(name).undefine()
 
 
-class wvmNWFilter(wvmConnect):
+class wvmNWFilter(wvmNWFilters):
     """A filter of the host. A page reads its XML once (tree); a change is
     the filter defined again with its UUID, which libvirt does in place, also
     while a VM uses it, and refuses for XML it cannot parse or apply to the
     running VMs' interfaces."""
 
     def __init__(self, host, login, passwd, conn, nwfiltername):
-        wvmConnect.__init__(self, host, login, passwd, conn)
+        wvmNWFilters.__init__(self, host, login, passwd, conn)
         self.nwfilter = self.get_nwfilter(nwfiltername)
 
     @cached_property