[Feature request] - User-agent string profiles

[Model6s]

I would love to be able to change the user-agent string of every profile. One example of usefulness can be by opening a app with desktop / mobile mode. The second reason is, I use cursive.chrome.apps which is only available on ChromeOs. I know that you can add "u-a string" to <WebView> tag. I am not so sure about Iframes.

Thanks your plugin really upgraded my workflow.