Executing bash commands in the container

Right now, it's not possible to execute a bash command on the running container, since the `tail` command is executed in the interactive mode at startup (see [start.sh:23](https://github.com/AKSW/ontowiki.docker/blob/master/ubuntu-nginx/start.sh#L23)).

So with these changes the container can be run with the following set of commands:
* `docker -t -i -p 8080:80 ontowiki /bin/bash`
* _[in container]_ `./start.sh`

To detach from the container's shell press: `Ctrl+P and Ctrl+Q`.

In example, I want to be able to execute a bash command, because I need to set proxy setting at `config.ini`.