MsgBox sizing and rendering

[cursork]

A couple of issues:

The size of the box isn't dynamic (demo in ewc branch issue/msgbox-size )

{"WX":{"Info":[["MB1",150,300]],"WGID":"25"}} as a message from client to server doesn't give us much useful information in itself, we could make the Info just []?

The corners should only be rounded on the edges, not inside the message box. Setting border-top-left-radius and border-top-right-radius to zero, for the bottom section containing the buttons, for example. Reverse that for the top.