Change repository "Clone/Checkout As" to "Short Name"

Summary:
Ref T4245.

  - Rename "Clone/Checkout As" to "Short Name" in the UI.
  - Allow any repository to have a short name, not just hosted repositories.

Test Plan:
  - Ran migration.
  - Reviewed old transactions, saw they looked good.
  - Edited an existing repository's short name.
  - Gave an imported repository a new short name.
  - Removed a repository's short name.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4245

Differential Revision: https://secure.phabricator.com/D14989

resources/sql/autopatches/20160111.repo.01.slugx.sql

@@ -0,0 +1,2 @@
+UPDATE {$NAMESPACE}_repository.repository_transaction
+  SET transactionType = 'repo:slug' WHERE transactionType = 'repo:clone-name';