Update site_path handling in gruntfile

[dankeemahill]

In order to make it clear and simple to specify where a project is staged and deployed,

• organize site_path configuration in Gruntfile
• update readme
• set site path where it belongs in other places, like index.php

[dankeemahill]

@cjwinchester might have the index.php step working in https://github.com/statesman/archieml-test