ui: lxc/qemu: add disk reassign and action submenu

ui: lxc/qemu: add disk reassign and action submenu

For the new HDReassign component, we follow the approach of HDMove to
have one componend for qemu and lxc.

To avoid button clutter, a new "Disk/Volume action" button is
introduced. It holds the Move, Reassign and Resize buttons in a
sub-menu.

Signed-off-by: Aaron Lauterer <a.lauterer@proxmox.com>
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Reviewed-by: Fabian Ebner <f.ebner@proxmox.com>