Group json-requests / Batch requests

[zeisss]

Currently we fire off one http request per JSON Call. When finishing an edit this leads to four (4) concurrent requests for a short period of time.

We should add a slight delay (50-100ms) and group requests into batches. The endpoint.php script already supports these. We just have to implement them on the client.

[zeisss]

Closed due to inactivity.