Some UI-related improvements for 0.1.3

* Gets rid of the "Unblock my blocked sites" button, since this seems to not be useful to users.
* Adds "Disable on this page" button to settings menu, since some users are essentially looking for this functionality when they click on the settings button.
* Makes "Unblock all" functionality more clear.
* Minor modifications to firstRun.html from the Chrome port.

If I have time, I will try to also fix #100 before making a release today.