R1:e4eeff814013

Use remarkup rule priorities in Phabricator

Summary:
Depends on D6329. This fixes `http://www.example.com/D123`, which currently gets the "D123" rendered, after addition of the Asana rule. It also removes a hack for object refernces.

Basically, the "hyperlink" rule needs to happen after rules which specialize hyperlinks (Youtube, Asana) but before rules which apply to general text (like the Differential and Maniphest rules). Allow these rules to specify that they have higher or lower priority.

Test Plan…