Add virtual scrolling to the Gallery

[dnns92]

• [X] I have searched to see if a similar issue already exists.

Is your feature request related to a problem? Please describe.
For large datasets that are accessed from a remote source, e.g. via sockets, I do not want to load the data at once, but incrementally depending what the user wants to see right nwo.

Describe the solution you'd like
For large datsets that are received from a remote source, it's necessary to not load it all in one instance, but depending on the gallery slider position. For this to work, we need two things:

• Scale the slider according to the full size of the dataset
• Provide an event where the slider position is returned if changed, and the gallery values can be changed or the values can be used as an input for a new gallery object.

Additional context
This is often referred to as virtual scrolling

[pngwn]

We do this for the Dataframe and virtual scrolling for images is significantly easier technically, so this seems reasonable.