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/types/common.go

@@ -98,6 +98,8 @@ type IGuiCommon interface {
 	KeybindingsOpts() KeybindingsOpts
 	CallKeybindingHandler(binding *Binding) error
 
+	ResetKeybindings() error
+
 	// hopefully we can remove this once we've moved all our keybinding stuff out of the gui god struct.
 	GetInitialKeybindingsWithCustomCommands() ([]*Binding, []*gocui.ViewMouseBinding)