chroot jail development environment option

I can't use Vagrant and VirtualBox in Qubes. I also realized that I can't use it on an older PC I have running Ubuntu because it doesn't support 64-bit hardware virtualization. So I made an ubuntu precise development environment that doesn't rely on VMs, and uses chroot jails instead.

This fixes #347.

Also it includes a cool script to make things easier:

    [user@dev securedrop]$ ./chroot-dev 
    Usage: ./chroot-dev [command]
    
        up      # create chroot if needed, mount filesystems, start servers
        down    # stop servers, unmount filesystems from chroot
        start   # start securedrop web app servers
        stop    # stop securedrop web app servers
        restart # restart securedrop web app servers
        test    # run tests
        destroy # destroy chroot jail