[Feature request] Indicate on toolbar icon that site in currently active tab is supported or not

[barszczmm]

Hi.

Your great extension supports over 30 websites and you will probably add more. It's impossible to remember where this extension should work and where not. It would be very useful if icon in toolbar could be grayed on not supported websites and colored on supported (or could have some green checkmark on supported websites). This way user would instantly know that currently visited site is supported. Currently user have to click on icon and then see if "Play now", "Queue" and other buttons are disabled or enabled.

I think that would be great usability improvement.

[maciex]

Pull request #134 addresses exactly this issue.