Extended customizability of $resource

Added an option to $resource's `action` parameters.  The user can define a custom httpConfig and a custom parseResponse function.  These allow the user to work with a lot more systems (sending custom headers through action.httpConfig and parsing weird responses with parseResponse).

Example use case.  these additions let me use www.parse.com and $resource together easily.
```javascript
var myHttpConfig = { headers: myHeaders }; //Our pre-defined custom headers to use parse.com
var ParseResource = $resource('https://api.parse.com/1/classes/:class/:id', {
  class: '@class',
  id: '@id',
}, {
  get: { method: 'GET', httpConfig: myHttpConfig },
  create: { method: 'POST', httpConfig: myHttpConfig },
  save: { method: 'PUT', httpConfig: myHttpConfig },
  query: { 
    httpConfig: myHttpConfig,
    isArray: true,
    // Parse.com's response from a query is stored in response.data.result,
    // a parseResponse function allows us to use this
    parseResponse: function(response) {
      return response.data.result;
    }
  }, 
  remove: { method: 'DELETE', httpConfig: myHttpConfig }
});
```

I don't know if action.httpConfig and action.parseResponse are the best names, but I think the idea of adding these two simple things adds a lot more flexibility to $resource.