New Feature: new PGN window button to access Lichess Opening Explorer data

[whelanh]

Thanks to a user request, a new button "Lichess OpenExplorer" has been added to the PGN window. To use it, you must have a lichess API key which is easily obtained.

The pop-up dialog preserves all the choices you can make on Lichess. If you use the Options/Save Options menu choice, you can save all of your preferences and your API key (locally on your machine).

You have the choice to search the current position in the Masters Database, the Lichess Games database, or the Player database (using the player username). Note: the Player database query is slow...but it does work!

If you double-click on one of the listed games, you can load it into the clipbase.

Illustrations of the new feature are shown below: