Local demos now using local assets and runs a server

I think logging here is probably the wrong thing to do (also on line 53).  The reason is that we're buffering stderr and stdout specifically to hide the output of the command line application.  If there is a problem we can then decide to display the contents of the stderr buffer.  With this method, there is a potential for interleaved output between processes which could confuse things further.  I'll look at better errors in issue #3.