Allow for navigation to empty path auxiliary routes

[danielwiehl]

Is your feature request related to a problem? Please describe.

The workbench router does not yet support navigating to "named views" with an empty path.

Describe the solution you'd like

The workbench router allows navigating to named views with an empty path.

Example for navigating to the following route

// Route
const route: Route = {path: '', outlet: 'outline', component: OutlineComponent};
// Navigation
inject(WorkbenchRouter).navigate([''], {target: 'outline'});