Implemented nsRouterLinkActive directive (angular2 routerLinkActive)

[ntrp]

The directive works exactly as the angular default one.

Didn't create tests yet but if needed I can look into it maybe. To test it yourself you can just add the directive to some routing links and verify that the class is added (also works on ancestor):

<StackLayout horizzontalAlign="left">
    <Label text="Home" [nsRouterLinkActive]="['selected']" [nsRouterLink]="['/home']"></Label>
    <Label text="Test" [nsRouterLinkActive]="['selected']" [nsRouterLink]="['/test']"></Label>
</StackLayout>

[ntrp]

Needed by the nsRouterLinkActive directive while processing the reduceList function:

https://github.com/ntrp/nativescript-angular/blob/f78b8e874eb0aab3b42cd6c04c7abf44ec7f5768/nativescript-angular/router/ns-router-link-active.ts#L99

[vakrilov]

👍