Show settings after first install, new features list with images after update

[IndrekV]

Should show welcome page and settings.

Maybe show settings page with added descriptions.

Example:

chrome.runtime.onInstalled.addListener(function (object) {
    chrome.tabs.create({url: "http://yoursite.com/"}, function (tab) {
        console.log("New tab launched with http://yoursite.com/");
    });
});

[tcrammond]

Closing in favour of #1199 for second part.