* Adds a limit of parallel preview requests to prevent the server from being overrun with requests
* Cancels ongoing and queued preview requests when they are aborted (e.g. when leaving the page)
* Adds lazy loading for space images
* Prevents the image resource from being fetched for each space
* Uses caching for space images

Also introduces a global `loadPreview` method and removes the visibility observers in each view. Previews are now loaded event-based instead, which should result in a better performance overall.

Removes this feature as it only adds complexity and very little value.