Allow calling lightbox methods from other places

[AndBondStyle]

When using mkdocs-material or instant navigation, plugin injects a script that looks like this:

document$.subscribe(() => { const lightbox = GLightbox(...); });

Instead, I suggest to insert this, making the lightbox variable accessible from outside:

const lightbox = GLightbox(...);
document$.subscribe(() => { lightbox.reload() });

This makes possible to call various methods of the lightbox instance from other JS scripts.

[blueswen]

LGTM! Thanks for your help.