Add ip camera streaming support

[ljcmps01]

I'm running a few instances of octoprint and the custom services is nice and all (though, having both text and bar as display parameters would be great), but what I really like to have is a card/widget to visualize my mjpeg stream

Having a custom service to attach a stream url would be great, that way I can monitor my prints from the dashboard, also obviously that be handy for those who have ip cameras accross in their setup