Revert "nixos: Remove torify module"

tsocks is still useful because it's less strict

This reverts commit 1b26faeb6994151b8f8842f340fe4c1b820f09fb.
tor: restore strong circuit isolation
tor: restore the Privoxy setup, but configure the system Privoxy instead of running a separate instance.
torsocks: enable by default if tor client functionality is enabled
rename torify to tsocks, to avoid name clashes and make it clear which wrapper library is used
resurrect torsocks-faster