Add options button to welcome page

[WesleyBranton]

When the user first installs the add-on, a welcome page is opened along with the add-on options page. An issue with this approach (specifically on Firefox) is if the user checks the option to allow the add-on to run in Private Browsing mode (which the browser prompts them to do), the add-on is restarted and the options page is therefore closed.

Using the same technique as the unsubscribe options added to the bottom of the add-on update notifications pages, a button could be added to the welcome page that will open the add-on options page. This will help solve the problem above because the welcome page does not close when the add-on is restarted by the browser.