Parse optional named filters from filter url

Old format fltN_M still works, but the new format flt_name_operation coexists side-by-side.

flask_admin/model/base.py

@@ -958,27 +958,34 @@ class BaseModelView(BaseView, ActionsMixin):
         sort_desc = request.args.get('desc', None, type=int)
         search = request.args.get('search', None)
 
+        filter_idx_by_label = dict((flt.query_label(), i) for i, flt in enumerate(self._filters))
         # Gather filters
         if self._filters:
             sfilters = []
 
             for n in request.args:
-                if n.startswith('flt'):
-                    ofs = n.find('_')
-                    if ofs == -1:
+                if not n.startswith('flt'):
                     continue
 
+                pos, filter_label = n[3:].split('_', 1)
+                
+                # If pos not specified, just add incrementally to the list.
+                pos = int(pos) if pos else len(sfilters)
+
                 try:
-                        pos = int(n[3:ofs])
-                        idx = int(n[ofs + 1:])
+                    # See if filter is numeric
+                    idx = int(filter_label)
                 except ValueError:
+                    # If non-numeric, look filter up by name
+                    try:
+                        idx = filter_idx_by_label[filter_label]
+                    except KeyError:
+                        # No matching filter name
                         continue
 
-                    if idx >= 0 and idx < len(self._filters):
+                if 0 <= idx < len(self._filters):
                     flt = self._filters[idx]
-
                     value = request.args[n]
-
                     if flt.validate(value):
                         sfilters.append((pos, (idx, flt.clean(value))))