Add connect task into grunt watch to start developer server

Hi everyone.
I suggest to add [connect](https://github.com/gruntjs/grunt-contrib-connect) task into Gruntfile to start local server when `grunt watch` happened. In build.config.js I've added server setting for configure hostname and port.
I think, it will be more useful than ```cd build && python -m SimpleHTTPServer 8080``` (for e.x.), because with `grunt connect` we able to configure [proxy](https://github.com/drewzboto/grunt-connect-proxy) for work with some api.