Adds HTTPHeaders for playing from http source

[igorkravchenko]

Sometimes it is required to send HTTP headers along with URL. Is there a chance we can add this?

[mmcdole]

👍 this would be amazing.

[sadhiappan]

I often have to play mp3s from sources that require oauth authorization headers.  This would help me out a lot. The changes made my @igorkravchenko looks pretty clean. Would love to have it in master.

[ap4y]

For some reason I missed this PR, I think I was on vacation around that time :) Will merge in next couple days.

[igorkravchenko]

Still on vacation? ;)

[ap4y]

Sorry for not responding previously. I didn't merge this PR because I didn't like idea of having plugin specific options on engine mediator (plus some code styling issues). I tried to draft different implementation, but got sidetracked as always. Right now I'm not too interested in investing much time into new features, as described here. If someone needs this feature, I think it should be ok to use your branch or fork and patch.