Add option to reset all levels

Currently the only way to reset the status for all levels is manually selecting them, seeing the solution and then pressing reset.
It would be useful to have a replay functionality.
Just add a Reset all button under the choose level dialog with a little confirmation dialog.

[sharkdp]

Thanks for the feature request. I'll think about it.

In the meantime, you can always reset the localStorage in your browser, which will have the same effect. You can do so by using the developer tools in your browser, or by calling localStorage.clear() from the dev console.