How to set Spotify as a default player?

I would like to set Spotify as a default player to be able start or reasume playing by Start button in bluetooth device. There is no such option in Spotify. I have installed Default App Manager and Spotify does not appear on list in Audio nor Audio Streaming Category. Instaed of I can see e.g. Google Music. 

Why Google Music can be default player but not Spotify?

It's very annoying when during driving have go to the menu, run Spotify and click play to play music. 

BTW. When Spotify is running and playing control buttons at bluetooth device are working well. But when I run Spotify by e.g. Trigger app bluetooth control button does not work until I click Play in Spotify.