feature: re-order displayed metrics based on file-list order

This commit re-orders the displayed metrics "sloc, lint errors, etc" based
on the selected file-list ordering. This is done by moving the appropriate
element via jQuery inside the DOM.

  * update casper-options in Gruntfile
  * add test for "ordered metrics" feature
  * update "plator-sortable-file-list.js" with new sorting feature
  * update "Contributors" in README.md

A test using 'CasperJs' is also included and can be run with

```
$ casperjs test test/casper-sortable-metrics.js
```

regards