Add lookupTitle attribute

This is the normalized title without the fragment, which is what
should be used for existence check purposes. Also add a test for
an internal link to a page's section.

Change-Id: I0e04f64c1bebeff84a0c17ef9b6c8dc06876f769
Display links to nonexistent pages as red

* Add ve.init.mw.LinkCache to track page existence and
  transparently query it
* Populate it with initial data from the parser cache
  if available, obtained in the VE API module
* Use linkCache data in link annotation rendering

This doesn't yet integrate the LinkCache with other
components like the link inspector. That should be
done so we can deduplicate the existence checks.

Additionally, we should generalize LinkCache and use
it for the category existence/status checks as well.

Bug: 37901
Change-Id: I9fd43e8c3864dd375cf6dadfdeedd05e4fe9cf3b
Merge "Add lookupTitle attribute"
Merge "Display links to nonexistent pages as red"