Download commands: Add JGit archive

Since JGit 3.1 archive command was implemented. Add it to download
drop down as new line.

The following libraries are introduced in this change:

* jgit-archive (Apache 2)
* commons-compress (Apache 2)
* tukaani-xz (Public domain)

Change-Id: I5f61aac8c434414c73585a9320e84f4430dd111d

lib/jgit/BUCK

@@ -33,6 +33,23 @@ maven_jar(
   ],
 )
 
+maven_jar(
+  name = 'jgit-archive',
+  id = 'org.eclipse.jgit:org.eclipse.jgit.archive:' + VERS,
+  sha1 = 'c645b284344ec9791404f6fd0e04f6dbedb58b7d',
+  license = 'jgit',
+  repository = REPO,
+  deps = [':jgit',
+    '//lib/commons:compress',
+    '//lib:tukaani-xz',
+  ],
+  unsign = True,
+  exclude = [
+    'about.html',
+    'plugin.properties',
+  ],
+)
+
 maven_jar(
   name = 'junit',
   id = 'org.eclipse.jgit:org.eclipse.jgit.junit:' + VERS,