Limit number of parallel expensive requests

When scrolling through search results in the clients, the preview images can take long to load, and by scrolling you create more requests than any backend can handle.

Part 1 of this ticket is to do some kind of request limitation in the frontend, e.g. 4 or 8 parallel requests.

When you scroll down e.g. through 50 items, those items will be loaded in order. this means that the items at the bottom (the one the user currently sees) are loaded last.

Part 2 of this ticket is is optimize this: Send the most recent requests first (last in - first out).