add a setting for local cursor

add a setting for local cursor

noVNC logic is this: do not show a local cursor, except when the server
sends it

this cannot happen with qemu (excluding QXL) and so we only ever have
the remote cursor.

since that is sometimes very laggy, add the option to show the local
cursor in addition

this reinstates the old behaviour where the user would (normally)
see two mouse cursors: one remote and one local, but since
this can be configured now, users which do not want this can
turn it off

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>