Initial XULRunner Support

make now generates a XULRunner application as well as a Firefox extension.  The XULRunner application works for me, although it has a few bugs and is definitely not ready for production use.

BETA TESTERS: The main feature that we need tested is HTTPS .bit websites with the standalone proxy.  Two known sites are https://dot-bit.bit/ and https://www.freespeechme.bit/ .  Please let us know if these work once the TLS installation script has been executed.  (Windows, Ubuntu, and Fedora are the operating systems that hopefully work.)  Also, report any bugs introduced in this PR.