Starting Node Inspector if available

Hi,

   I am not sure if it has its place here or if it should be done in a more customised way (Like in Grunt or something) but I found it very handy to have ```node-inspector``` started alongside ```sails debug```

   This patch is modifying ```sails-debug``` script to do just that but only if ```node-inspector``` is present in the dependencies.

   The caveat is that I wasn't sure how to access the configuration files in here, so the inspector is running with the default parameters.
   I would happy to make it configurable if you have an idea how.
   Via config file, sails.rc or command line options maybe?