refactor(Location): out of router and into platform/common

closes https://github.com/angular/angular/issues/4943

BREAKING CHANGE:

`Location` and other related providers have been moved out of `router` and into `platform/common`. `BrowserPlatformLocation` is not meant to be used directly however advanced configurations may use it via the following import change.

Before:

```
import {
  PlatformLocation,
  Location,
  LocationStrategy,
  HashLocationStrategy,
  PathLocationStrategy,
  APP_BASE_HREF}
from 'angular2/router';

import {BrowserPlatformLocation} from 'angular2/src/router/location/browser_platform_location';
```

After:

```
import {
  PlatformLocation,
  Location,
  LocationStrategy,
  HashLocationStrategy,
  PathLocationStrategy,
  APP_BASE_HREF}
from 'angular2/platform/common';

import {BrowserPlatformLocation} from 'angular2/src/platform/browser/location/browser_platform_location';
```

Closes #7962

modules/angular2/platform/common.ts

@@ -0,0 +1,5 @@
+/**
+ * Platform agnostic services.
+ * Can be used both in the browser and on the server.
+ */
+export * from 'angular2/src/platform/location';

modules/angular2/platform/common_dom.ts

@@ -1,5 +1,6 @@
 /**
- * This is a set of classes and objects that can be used both in the browser and on the server.
+ * This is a set of DOM related classes and objects that can be used both in the browser and on the
+ * server.
  */
 export {DOM, setRootDomAdapter, DomAdapter} from 'angular2/src/platform/dom/dom_adapter';
 export {DomRenderer} from 'angular2/src/platform/dom/dom_renderer';

modules/angular2/platform/testing/browser_static.ts

@@ -14,7 +14,7 @@ import {MockAnimationBuilder} from 'angular2/src/mock/animation_builder_mock';
 import {MockDirectiveResolver} from 'angular2/src/mock/directive_resolver_mock';
 import {MockViewResolver} from 'angular2/src/mock/view_resolver_mock';
 import {MockLocationStrategy} from 'angular2/src/mock/mock_location_strategy';
-import {LocationStrategy} from 'angular2/src/router/location/location_strategy';
+import {LocationStrategy} from 'angular2/platform/common';
 import {MockNgZone} from 'angular2/src/mock/ng_zone_mock';
 
 import {XHRImpl} from "angular2/src/platform/browser/xhr_impl";

modules/angular2/platform/testing/server.ts

@@ -16,7 +16,6 @@ import {MockAnimationBuilder} from 'angular2/src/mock/animation_builder_mock';
 import {MockDirectiveResolver} from 'angular2/src/mock/directive_resolver_mock';
 import {MockViewResolver} from 'angular2/src/mock/view_resolver_mock';
 import {MockLocationStrategy} from 'angular2/src/mock/mock_location_strategy';
-import {LocationStrategy} from 'angular2/src/router/location/location_strategy';
 import {MockNgZone} from 'angular2/src/mock/ng_zone_mock';
 
 import {TestComponentBuilder} from 'angular2/src/testing/test_component_builder';
@@ -36,6 +35,7 @@ import {
   ELEMENT_PROBE_PROVIDERS
 } from 'angular2/platform/common_dom';
 import {DomEventsPlugin} from 'angular2/src/platform/dom/events/dom_events';
+import {LocationStrategy} from 'angular2/platform/common';
 
 import {CONST_EXPR} from 'angular2/src/facade/lang';