Add grunt serve task that starts a livereloading webserver and watches source files for changes

This adds a new task `grunt serve`, that
* builds the NEXT library
* starts a connect based webserver on port 9000 to serve the root of the EaselJS folder (locally accessible only)
* opens a browser window to the above
* watches the source files, automatically triggering a NEXT rebuild if they change
* livereloads the served pages whenever a html/css/js/etc file changes

An `npm install` in the build directory will be required.   Typical usage is to have it running in the background while you're developing/debugging.  
Sure.  I'm interpreting this and the above watch change as don't do the docs.  Everything else seems to be necessary.  So both would be replaced with along along the lines of `'updateversion', 'combine', 'uglify', 'clearversion', 'copy:src'`.  Agreed?