Add Ctrl-o as a Shortcut to Load an SGF File

[psygo]

I think most software uses Ctrl-o as a combination to open files. Since it's not being used right now by KaTrain, could we maybe overload it with the current Ctrl-l?

[psygo]

The same thing goes for "Save Game As...", which is usually done with Ctrl-Shift-s.

[github-actions]

This issue is stale because it has been open 90 days with no activity. Remove stale label or comment or this will be closed in 10 days.

[Zaoliang]

fully agree with ctrl-o

[github-actions]

This issue is stale because it has been open 90 days with no activity. Remove stale label or comment or this will be closed in 10 days.