Installation updates

Updates the default installation location to the conda environment /bin. This eliminates the need to source bayeswave-user-env.sh, and works with the condor updates that can't use get_env=True any more. User can still specify a specific installation directory if needed; in this case you will still need to source bayeswave-user-env.sh for the python utilities to work.

@james-clark and @sophie.hourihane can one or both of you check whether this makes sense, and maybe see if you can install without any issues?