Open 'Read the Bill' in a new tab/window?

[aih]

The link to the Read the Bill button currently opens Govtrack text for the bill update in the same tab (#274). Do we want this to open in a separate tab, so the user still has the billmap page, or do we want to leave it as is?

To open in a new tab/window, add target="_blank" and rel="noopener noreferrer" to the anchor tag