Add a watch task for copying files.

Previously, `grunt server` would serve files from the `./deploy/static/` folder, and if a file was not found, [would fall back to serving that file from the `./static/` folder](https://github.com/ff0000/generator-red-static/blob/e60ae421c087bced92232b1f32db5d8098458cb8/app/templates/grunt/config/connect.js#L23-L24).

This has the side effect of breaking builds on deployment when some files were not specified in the copy task.

In the `0.2.0` version, the server [will only watch the `/deploy/static/` folder](https://github.com/ff0000/generator-red-static/blob/444e2e8ee928793a0a05f1d988bc4aefa2594449/app/templates/grunt/config/connect.js#L13). Now, however, whenever there are changes to files in the copy task, they will not be updated until the next time `grunt copy` is run.

This PR adds a watcher for files in the copy task. Also, rather than copying all files any time one of the files changed, `grunt-newer` was added to only copy the newly changed files.