webadmin: GUI support for setting the new VmPool.maxAssignedVmsPerUser property

Added textbox to VmPool New and Edit dialog for setting the new
maxAssignedVmsPerUser property

Change-Id: Ic92e98c87a72326b14a7ae002353cf720f3c9605
Signed-off-by: Martin Betak <mbetak@redhat.com>