make hiding unmatched rapid hints configurable

qutebrowser/browser/hints.py

@@ -765,8 +765,9 @@ class HintManager(QObject):
                         self._show_elem(elem.label)
                 else:
                     # element doesn't match anymore -> hide it, unless in rapid
-                    # hinting mode (see #1799)
-                    if not self._context.rapid:
+                    # mode and hide-unmatched-rapid-hints is false (see #1799)
+                    if (not self._context.rapid or
+                            config.get('hints', 'hide-unmatched-rapid-hints')):
                         self._hide_elem(elem.label)
             except webelem.Error:
                 pass

qutebrowser/config/configdata.py

@@ -956,6 +956,10 @@ def data(readonly=False):
                  )), 'python'),
              "Which implementation to use to find elements to hint."),
 
+            ('hide-unmatched-rapid-hints',
+             SettingValue(typ.Bool(), 'true'),
+             "Controls hiding unmatched hints in rapid mode."),
+
             readonly=readonly
         )),