Free shipping possible: disable other shipping methods except self-collection

We are adding a new switch to the “freeamount” shipping module, i.e. free shipping. If this is activated, other shipping methods are automatically hidden as soon as the value for free shipping is reached. 
Of course, we take into account the countries for which free shipping is enabled and also the free shipping <-> self-collection configuration already available in Modified. So you can of course continue to enable self-collection if you wish.