A formater can generate HTTP redirect now.

This is usefule for result formaters.

To make the framework more generic. The final plan is to move the
generic server code to package pve-common.
Signed-off-by: Dietmar Maurer <dietmar@proxmox.com>

Signed-off-by: Dietmar Maurer <dietmar@proxmox.com>

To avoid GUI bugs with IE

As suggested by Michael in the forum.

Some clients need this to correctly interpret multipart messages.

So that we can see overall usage.