Add netsim support to base image

As covered in issue #242

This pull request adds support for netsim to the base image. In my tests, I found netsim requires make, libxml2-utils and xsltproc to successfully build and run netsims for the most common NEDs. So I've moved these packages from the dev image to the base image. In addition, netsim requires the ned-id xsl script from the support directory, so I've kept this directory in the base image. On my system, these changes caused the base image size to increase slightly from 581MB to 584MB.

Netsim can be started in a pre-ncs-start.d script, however there is currently no way to stop it when NSO stops. So I've modified the run-nso.sh to automatically start and stop netsim if the netsim directory exists. If we don't want to explicitly start and stop netsim from this script, we could change it to provide a ncs-stop hook allowing a custom script to be added to stop netsim.