Improve the picker for the page to relate to

Currently, when picking a page to make a relation to (from the current page), the UI displays a suggest of page references, including all pages from the wiki (hidden pages too).

This picker should be improved to meet the following:

• take into account the hidden setting for the current user: if the user did not configure his profile to activate viewing hidden pages, we should not display hidden pages for them
• it should show document titles and not references (notably for hiding .WebHome but also for respecting the rule that we show page titles everywhere in the UI, not names)
• it would be interesting to be able to relate to a page in a different wiki

The tree page picker (the one used to pick page locations when making a copy or a rename) seems like a good UI component for this, however the idea that we can type directly and get suggestions is very very interesting.
Maybe we can use a filterable tree as follows: when clicking on [+] we'd get a dialog with the page tree in which one can search, and upon confirming the selection in the tree, the relation would be created. It uses as many clicks as today and has suggest tool incorporated.