Move back to using Chrome on OSX closes #2043

This moves back to using Chrome on OSX but making it obvious that it's Chrome to avoid any user issues with running Chrome itself. This also includes a more general refactoring of the browser launching code, as it had gotten a little convoluted after various revisions. This should be a bit more maintainable and portable.
Oh gotcha. I got confused by the "have it take care of finding the chrome executable from amongst all possible paths" part, which to me we wouldn't want in that method. Changing the method name and adding a boolean flag would be fine, although I also kind of like having each OS-specific class be super explicit about whether or not they want it to be an app or not. With only three classes total, it doesn't seem like we'd be saving much with doing that part in BrowserUtils.