Update sheets asynchronously

Right now if I want to modify a character (open the sheet, then set an aura, or status, or HP or visibility, etc), I have to wait a bit until the data is synchronized with the server, before I can close the sheet.
This is annoying, beacuse it makes the GM (or PC) also synchronously wait for it to happen, delaying actual RP.

These calls could be made asynchronous, so we don’t need to wait - the show can go on.