Seek actions dispatched by waveform returning unresolved promises

[minuminukim]

When a mousedown event fires on the waveform, dispatching a seek action, console emits an error:
"Uncaught (in promise) DOMException: The play() request was interrupted by a call to pause(). https://goo.gl/LdLk22"

This doesn't cause the application to crash but should look into this. audio.play() and audio.pause() methods are asynchronous.

When a track is currently selected, but the player is paused, a seek event on the waveform should dispatch a play action.