feat(filterFilter): support deeply nested predicate objects

Due to 339a165, it became impossible to filter nested properties of an object using the filterFilter.
A proposed solution to this was to enable the use of nested predicate objects. This change enables the
use of these nested predicate objects.

Example:

```html
<div ng-repeat="it in items | filter:{ address: { country: 'Canuckistan'}}"></div>
```

Or

```js
$filter('filter')(items, { address: { country: 'Canuckistan' } });
```

Closes #6215
Related to #6009

test/ng/filter/filterSpec.js

@@ -70,6 +70,17 @@ describe('Filter: filter', function() {
   });
 
 
+  it('should support deep predicate objects', function() {
+    var items = [{person: {name: 'John'}},
+                 {person: {name: 'Rita'}},
+                 {person: {name: 'Billy'}},
+                 {person: {name: 'Joan'}}];
+    expect(filter(items, {person: {name: 'Jo'}}).length).toBe(2);
+    expect(filter(items, {person: {name: 'Jo'}})).toEqual([
+      {person: {name: 'John'}}, {person: {name: 'Joan'}}]);
+  });
+
+
   it('should match any properties for given "$" property', function() {
     var items = [{first: 'tom', last: 'hevery'},
                  {first: 'adam', last: 'hevery', alias: 'tom', done: false},