Add recent files menu and store recently opened files

[qcgm1978]

This commit adds a "Recent Files" submenu to the "File" menu that displays recently opened SGF files. It also stores the list of recent files in the browser storage and updates it whenever a new file is loaded, so the recent files stay in sync across browser sessions.

[kaorahi]

I pushed a few commits into your branch. Would you test them? Does my modification work well?

[qcgm1978]

No problem. I checked it and it works well.

[kaorahi]

Thanks for your contribution!