Replace "Share page" checkboxes, with a Select2-based autoselect.

On the "Edit -> share page" screen, we've got a series of checkboxes, one for every collection and non-collectioned page in your portfolio. The checkboxes are used for setting permissions in bulk.

The problem is that this is cumbersome and confusing, especially when you've got dozens of pages & collections.

I would like to replace these checkboxes with a multi-select select2 element. This could either be an AJAX-based autocomplete, or a simple multi-<select> element (which select2 will automatically transform to act Ajaxy).