Use ListItemsManager in messaging pages

Some messaging pages use split view, but they aren't using a ListItemsManager to manage the items like it's done in other pages with split view. This caused a bug (MOBILE-4249), a temporary fix was applied to correct the issue but ideally we should be using the items manager to make it more coherent with the rest of pages.

Here's a WIP commit to apply it in contacts page:

https://github.com/dpalou/moodleapp/commit/f35539995714b334e0faf1d8da6e86c9ccd6a925