Updates dockerfile

This provides a clean build by running the `bootstrap-bce.sh` on Ubuntu 14.04 (previous Dockerfile built on my existing RStudio image instead).  It then adds RStudio-server for interactive access, along with ssh and ipython-notebooks.  (Users can choose not to expose any of these services by simply not exporting the required ports).  

Had to install a few extra dependencies on top of the vanilla Ubuntu 14.04 to get bootstrap-bce.sh to run without error, not sure why.

This PR adds two extra files that the Dockerfile uses to configure and run things at setup, hope that's ok.  Otherwise it relies entirely on reusing the current scripts.

I tried to have the Dockerfile set up the secure ipython-notebook server using the script you've already provided, but for some reason could not get that to work. 

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Quick usage notes:

Launch the image from any platform that has docker installed: 

    docker run -d -p 8787:8787 -p 2200:22 -p 8888:8888 -e USER=<username> -e PASSWORD=<password> --name bce cboettig/bce

If using boot2docker, look up `<ip-address>` with command: `boot2docker ip`. On a linux, `<ip-address>` is `localhost`.
 
- Connect to RStudio-server: go to `http://<ip-address>:8787`  and log in with the user and password given.
- Connect to an ssh session:  `ssh -p 2200 username@localhost`.  (Note, no root privileges)
- Connect to an ipython session: go to `http://<ip-address>:8888`.  (Currently unsecured, do not expose an ipython port on a public host/cloud machine)