LinkFilter: version 3.0 - modernization & general fixes.

Sajax stuff replaced by a new API module (bug #53119), fixes to
LinkPage.php to make it play nicely w/ ContentHandler (or rather, to make
it work like how it used to instead of not displaying most of the things
it should display), further jQuerification of the JS file and many
miscellaneous fixes all over the place.

Change-Id: I0b949b0b7e0e01c54c2dd8117cf068b83e71f337