Add "Clone As" to repositories and generate full clone commands in UI

Summary:
Ref T4175.

  - Add a configurable name for the clone-as directory, so you can have "Bits & Pieces" clone as "bits~n~pieces/" or simliar.
  - By default, use "reasonable" heruistics to choose such a name.
  - Generate a copy/pasteable clone commmand with this directory name.

Test Plan: Looked at some repositories.

Reviewers: btrahan, chad

Reviewed By: chad

CC: aran

Maniphest Tasks: T4175

Differential Revision: https://secure.phabricator.com/D8097

src/applications/diffusion/controller/DiffusionRepositoryEditMainController.php

@@ -253,6 +253,15 @@ final class DiffusionRepositoryEditMainController
     $view->addProperty(pht('Type'), $type);
     $view->addProperty(pht('Callsign'), $repository->getCallsign());
 
+
+    $clone_name = $repository->getDetail('clone-name');
+
+    $view->addProperty(
+      pht('Clone/Checkout As'),
+      $clone_name
+        ? $clone_name.'/'
+        : phutil_tag('em', array(), $repository->getCloneName().'/'));
+
     $project_phids = PhabricatorEdgeQuery::loadDestinationPHIDs(
       $repository->getPHID(),
       PhabricatorEdgeConfig::TYPE_OBJECT_HAS_PROJECT);