Change repository description from plain text to remarkup

Summary:
At one point this was sort of a one-line summary but it isn't really anymore (and doesn't appear on the list view). We could add a summary in the future if we wanted.

  - Change the control from a text area to a remarkup area.
  - Change the display to remarkup.

Test Plan:
{F44183}
{F44184}

Reviewers: chad, btrahan

Reviewed By: chad

CC: aran

Differential Revision: https://secure.phabricator.com/D6034

src/applications/diffusion/controller/DiffusionRepositoryEditBasicController.php

@@ -91,7 +91,7 @@ final class DiffusionRepositoryEditBasicController extends DiffusionController {
           ->setValue($v_name)
           ->setError($e_name))
       ->appendChild(
-        id(new AphrontFormTextAreaControl())
+        id(new PhabricatorRemarkupControl())
           ->setName('description')
           ->setLabel(pht('Description'))
           ->setValue($v_desc))