I see actions for navigateToURL and navigateToSobject, etc, but not NavigateToLightningApp?
navigateToComponent was the closest we had, and it's gone now. Right now your only option is to mount your Lightning Page or Component as a tab, and handle all navigation yourself by dynamically creating the components you desire.
Coming soon (hopefully) will be the ability to mount a lightning component as a
recordTab or as a quick action, but we don't have that yet.