Update the OMERO VirtualBox image

Not ready yet, but I'd like to get some feedback.

Main changes from the existing VM:
* Base image is [built using Veewee](https://github.com/manics/openmicroscopy/blob/omerovm_update/docs/install/VM/README.md#rebuilding-the-base-image). So far I've got a Ubuntu 13.04 64 bit and Debian 7.1 64 bit image, in theory it should be easy to build for other distros or 32 bit, just need some disk space. I've taken out the vagrant specific bits for now. Could be turned into a Hudson job.
* Cleaned up some of the installation scripts, deleted some stuff
* The omero user has sudo ALL=(ALL)NOPASSWD:ALL rights. This makes VM setup and configuration easier, if necessary it could be changed back to require a password after installation.
* No root login.
* OMERO dependencies are installed during the build, though it would be trivial to include them in the base image instead. What's better?
* Uses the distro supplied ice34 and openjdk-7-jre-headless.
* Postgres 9.1
* nginx is configured to run as a system service instead of being started by the omero user.
* pip and virtualenv are installed
* Current exported is ~1.4GB, existing VM is ~1.2GB, there might be scope for removing some unneeded packages.
* Not yet in the main build because it'll require configuration changes to the VirtualBox job, instead see http://hudson.openmicroscopy.org.uk/job/TEMPORARY-OMERO-merge-develop-virtualbox-NEW/

The naming convention is probably broken now if you run `./build.py build-vm` from openmicroscopy.git, e.g.
```
$ OMERO_JOB=OMERO-merge-develop-ice34 \
   OMERO_BASE_IMAGE=Debian-7.1.0-amd64-omerobase1.vdi \
   ./build.py build-vm
```
creates an image named `omero-vm-5.0.0-beta1-DEV-ice33.ova`

Is it worth moving the VM build scripts into a new repo, or omero-setup, since they're more or less independent of the OMERO codebase, and naming the image after the installed OMERO.server artifact instead?

A few possible issues:
* I get a unclean unmount warning when first booting the final VM image and I think there was some intermittent disk corruption occurring during the build with the Ubuntu image on gretzky, never had any problems running it on my Mac though. Coudl this be due to an old VirtualBox version (4.1 on Gretzky, latest is 4.2)
* Mismatch between versions of VirtualBox and VirtualBox guest additions, the version on Gretzky is 4.1 whereas the tools are 4.2.