Update existing Link Prompts

There are now UI buttons that create a new link prompt unlike the traditional link prompt. The new link prompt changed the title and the corresponding affirmation and cancellation buttons to now have "Open in browser" and "Cancel" accordingly. Compared to the old link prompt, with "Yes" and "No", these changes better reflect the intent of the link prompt.

Both types of link prompts exist in 18w43b.

The non-built-in link prompts should maintain the red warning message but be updated with the new title and buttons.