Don't allow opening a menu while the search or filter prompt is open

This solves several problems that arise from opening a menu while the prompt is
open. We might try to solve these in a different way, e.g. by dismissing the
search prompt before opening a menu, but restricting what you can do while the
prompt is open seems like the more robust fix.

To achieve this, we
- call resetKeyBindings both when opening and when closing the search/filter
  prompt
- change the keybindings to only contain the ones for the search prompt when
  that context is active.

pkg/gui/gui_common.go

@@ -140,6 +140,10 @@ func (self *guiCommon) CallKeybindingHandler(binding *types.Binding) error {
 	return self.gui.callKeybindingHandler(binding)
 }
 
+func (self *guiCommon) ResetKeybindings() error {
+	return self.gui.resetKeybindings()
+}
+
 func (self *guiCommon) IsAnyModeActive() bool {
 	return self.gui.helpers.Mode.IsAnyModeActive()
 }