[SDL 0288] Screen Manager Play Audio

Proposal: [Screen Manager Play Audio](https://github.com/smartdevicelink/sdl_evolution/blob/master/proposals/0288-screen-manager-play-audio.md)

> This proposal adds a `playAudio` method (based on the `Speak` RPC) to the screen manager.

Review: https://github.com/smartdevicelink/sdl_evolution/issues/962