Features/use config.params

This PR changes GET and DELETE to use the `config.params = {}` method of Angular which automatically stringifys the object and adds each key=>value as parameters to the query string. 

The advantage is that users can now intercept the params before the request is sent. 

The PR still supports using paramterized urls - if you define `show/:_id` or similar ngActiveResource will not use config.params. 

POSSIBLE BREAKING CHANGES
- Note that apps using the syntax of [:attrs] should remain unaffected, since we specifically check for `/:` to determine if we need to paramterize.
- Note that apps expecting intercept the url and see query params on the url itself will no longer work.