refactor(router): improve recognition and generation pipeline

This is a big change. @matsko also deserves much of the credit for the implementation.

Previously, `ComponentInstruction`s held all the state for async components.
Now, we introduce several subclasses for `Instruction` to describe each type of navigation.

BREAKING CHANGE:

Redirects now use the Link DSL syntax. Before:

```
@RouteConfig([
  { path: '/foo', redirectTo: '/bar' },
  { path: '/bar', component: BarCmp }
])
```

After:

```
@RouteConfig([
  { path: '/foo', redirectTo: ['Bar'] },
  { path: '/bar', component: BarCmp, name: 'Bar' }
])
```

BREAKING CHANGE:

This also introduces `useAsDefault` in the RouteConfig, which makes cases like lazy-loading
and encapsulating large routes with sub-routes easier.

Previously, you could use `redirectTo` like this to expand a URL like `/tab` to `/tab/posts`:

@RouteConfig([
  { path: '/tab', redirectTo: '/tab/users' }
  { path: '/tab', component: TabsCmp, name: 'Tab' }
])
AppCmp { ... }

Now the recommended way to handle this is case is to use `useAsDefault` like so:

```
@RouteConfig([
  { path: '/tab', component: TabsCmp, name: 'Tab' }
])
AppCmp { ... }

@RouteConfig([
  { path: '/posts', component: PostsCmp, useAsDefault: true, name: 'Posts' },
  { path: '/users', component: UsersCmp, name: 'Users' }
])
TabsCmp { ... }
```

In the above example, you can write just `['/Tab']` and the route `Users` is automatically selected as a child route.

Closes #4170
Closes #4490
Closes #4694
Closes #5200

Closes #5352

modules/angular2/test/router/router_spec.ts

@@ -18,7 +18,6 @@ import {ListWrapper} from 'angular2/src/facade/collection';
 import {Router, RootRouter} from 'angular2/src/router/router';
 import {SpyLocation} from 'angular2/src/mock/location_mock';
 import {Location} from 'angular2/src/router/location';
-import {stringifyInstruction} from 'angular2/src/router/instruction';
 
 import {RouteRegistry} from 'angular2/src/router/route_registry';
 import {RouteConfig, AsyncRoute, Route} from 'angular2/src/router/route_config_decorator';
@@ -225,6 +224,11 @@ export function main() {
   });
 }
 
+
+function stringifyInstruction(instruction): string {
+  return instruction.toRootUrl();
+}
+
 function loader(): Promise<Type> {
   return PromiseWrapper.resolve(DummyComponent);
 }