fix($resource): fix interceptors and success/error callbacks

Previously, action-specific interceptors and `success`/`error` callbacks
were executed in inconsistent relative orders and in a way that did not
meet the general expectation for interceptor behavior (e.g. ability to
recover from errors, performing asynchronous operations, etc).

This commit fixes the behavior to make it more consistent and expected.
The main differences are that `success`/`error` callbacks will now be
run _after_ `response`/`responseError` interceptors complete (even if
interceptors return a promise) and the correct callback will be called
based on the result of the interceptor (e.g. if the `responseError`
interceptor recovers from an error, the `success` callback will be
called).
See also angular#9334 (comment).

This commit also replaces the use of `success`/`error` callbacks in the
docs with using the returned promise.

Fixes angular#6731
Fixes angular#9334
Closes angular#6865

BREAKING CHANGE:

If you are not using `success` or `error` callbacks with `$resource`,
your app should not be affected by this change.

If you are using `success` or `error` callbacks (with or without
response interceptors), one (subtle) difference is that throwing an
error inside the callbacks will not propagate to the returned
`$promise`. Therefore, you should try to use the promises whenever
possible. E.g.:

```js
// Avoid
User.query(function onSuccess(users) { throw new Error(); }).
  $promise.
  catch(function onError() { /* Will not be called. */ });

// Prefer
User.query().
  $promise.
  then(function onSuccess(users) { throw new Error(); }).
  catch(function onError() { /* Will be called. */ });
```

Finally, if you are using `success` or `error` callbacks with response
interceptors, the callbacks will now always run _after_ the interceptors
(and wait for them to resolve in case they return a promise).
Previously, the `error` callback was called before the `responseError`
interceptor and the `success` callback was synchronously called after
the `response` interceptor. E.g.:

```js
var User = $resource('/api/users/:id', {id: '@id'}, {
  get: {
    method: 'get',
    interceptor: {
      response: function(response) {
        console.log('responseInterceptor-1');
        return $timeout(1000).then(function() {
          console.log('responseInterceptor-2');
          return response.resource;
        });
      },
      responseError: function(response) {
        console.log('responseErrorInterceptor-1');
        return $timeout(1000).then(function() {
          console.log('responseErrorInterceptor-2');
          return $q.reject('Ooops!');
        });
      }
    }
  }
});
var onSuccess = function(value) { console.log('successCallback', value); };
var onError = function(error) { console.log('errorCallback', error); };

// Assuming the following call is successful...
User.get({id: 1}, onSuccess, onError);
  // Old behavior:
  //   responseInterceptor-1
  //   successCallback, {/* Promise object */}
  //   responseInterceptor-2
  // New behavior:
  //   responseInterceptor-1
  //   responseInterceptor-2
  //   successCallback, {/* User object */}

// Assuming the following call returns an error...
User.get({id: 2}, onSuccess, onError);
  // Old behavior:
  //   errorCallback, {/* Response object */}
  //   responseErrorInterceptor-1
  //   responseErrorInterceptor-2
  // New behavior:
  //   responseErrorInterceptor-1
  //   responseErrorInterceptor-2
  //   errorCallback, Ooops!
```