DocPress updates

We've added a couple of new options to DocPress.it.

1. New link options:

• open all links in a new tab,
• apply 'nofollow' attribute to links

2. Add alt text to images for more SEO friendly articles directly from Google Docs.

These are applied directly from the options panel of the add-on.

We also fixed a couple of bugs, like when starting the add-on and deleting a website.