Updating Cheats manager when the ISO is changed etc.

### Non-modal dialogs

The Cheats manager dialog was made non-modal in 983d5d1f

The benefit with a non-modal dialog is the option to keep it open during emulation without

* blocking the main window
* disabling the hotkeys because the modal dialog receive keyboard input instead of the main window

Non-modal dialogs should be updated when the ISO is changed because that allow it to show information for the current ISO

### Cheats disabled

When "Config → General → Enable Cheats" is disabled

* the "Tools → Cheats Manager" menu option is disabled
* the Cheats Manager window is closed

because

* the cheats have no use during a running emulation in this case
* it'll otherwise show an empty "AR Codes" tab which incorrectly indicate that the ISO doesn't have AR codes

However because the dialog has a use for enabling/disabling cheats it could be useful to allow the dialog with "Config → General → Enable Cheats" disabled, this isn't done because

* it would require changes in "namespace ActionReplay" to load the codes when "Config → General → Enable Cheats" is disabled too