Anki add-on: AltGr keyboard shortcut workaround

This add-on prevents AltGr+alphanumeric keystrokes (eg AltGr+2 for '@', or AltGr+s on a Polish keyboard), when typed into a text editing box, from mistakenly triggering keyboard shortcuts in the review screen and browse screen. When installed, you will need to use Esc twice to close dialog boxes, and some add-on shortcuts that use the Alt key may stop working. Thanks to dlon for the implementation.