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
9 files changed