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';