Allow isolated instances

[berwyn]

A problem that I currently have is that I use Edge as an actual browser, and using this utility causes a new tab to pop in existing windows with no way to manage that individual tab. It'd be nice if there was a way to use this tool to create a dedicated window that an automated system (e.g. Karma) could manage without interfering with other Edge windows. Additionally, it'd be cool if we could launch an instance of Edge without the user's profile loaded, so that we could test without any extensions/userscripts interfering with the content under test.