Backlink Support

Adds wiki-link as default shift link to support new Bear backlinks in info tab (context).

An annoying caveat to this is that you must now cmd-click links to open them in a new window. @msageryd has made a feature request with Bear support to have "open links in new window" as a global Bear setting and they sound receptive to supporting it in future releases .

You can paste the previous default links with shift-cmd. Pasting ToC has been changed to option-cmd since it is less useful now with Bear 2's built-in ToC support.