[JS] Refactor module

I originally was going to provide a patch to just extend the current 7.x-1.x branch with a "sub-module" that was a very hackish way (wrapping callbacks) to provide token validation and $_POST parsing for AJAX requests.

After reviewing the code, I felt it was simply better and easier to just integrate these into the module itself. Also updating this module is painful because most of the code lives in the root js.php file. Each time it has to be updated. The code should also be refactored so it calls an execution function (just like index.php).

Solution/to-do:
Merge/update the 7.x-2.x branch with current 7.x-1.x code.
Refactor module.
Update documentation
Provide an example module for implementation
Create a dev release