Provide scripts for installing and running txircd standalone

Since Ashton asked about this, I wrote a few scripts to make running txircd standalone a bit more convenient. It handles setting up the virtualenv and provides an easy way to start and stop the deamon. It assumes python2-virtualenv, as well as the requirements for the dependencies txircd uses (these being a C compiler for Twisted, python2-dev, libssl-dev and libyaml-dev), are already installed on the system.
A thought occurs that I didn't have last time for some reason:

Do we need this check at all? `twistd` makes these checks for us anyway.