Create, delete, reorder and modify groups and layers.
There are still some issues:
A request may be misinterpreted by the server when 2 clients send move or delete requests at the same time. The 2nd request handled by the server will be wrong.
Clients need to wait for the server reply to refresh themselves after a modification and are frozen.
fixed #24
Create, delete, reorder and modify groups and layers.
There are still some issues: