Feat: `move_item_from_lista_to_listb/4` function for moving `items` between `lists`

[nelsonic]

To aid with _moving _an item from one list to another, we need a little function.

Todo

• [x] Create the tests: item.cid should be removed from lista and added to listb. 🧪
• [x] Write the function. 🧑‍💻
• [x] Ship!! :shipit:

Note: this only applies if the list is not "All" which we should not remove items from; That's the whole point of the "All" list ...

Thankfully we already have two helper functions we can call for this:

https://github.com/dwyl/mvp/blob/15af0f1158b00bc059bd7b2fc9c118ae4313fcbf/lib/app/list.ex#L171-L176

and:

https://github.com/dwyl/mvp/blob/15af0f1158b00bc059bd7b2fc9c118ae4313fcbf/lib/app/list.ex#L189-L199

So this should be relatively straightforward. 💭

[nelsonic]

This is the function:

  def move_item_from_lista_to_listb(item_cid, lista_cid, listb_cid, person_id) do
    # Remove from List A:
    remove_item_from_list(item_cid, lista_cid, person_id)
    # Add to List B:
    add_item_to_list(item_cid, listb_cid, person_id)
  end

Like I said above, it's simple. Because we already had the two precursor functions thanks to #422

But I'm now thinking that from an Interface perspective what we actually want to do is update the whole list.seq from the client so that we preserve the sequence of the items ... 💭

[nelsonic]

Included in #165 :shipit: If we decide not to use it, easy to remove. 👌