add ability to use a different ip address and port for bokeh-server

I added options ```--ip``` and ```--bokeh-port``` to bokeh-server. This is useful if you are working over ssh and need to view the plots on a different computer.

For instance,
```bokeh-server --ip 0.0.0.0 --bokeh-port 7000```

serves plots at:
http://name-of-my-server:7000/bokeh/