Improve the email notification content. Added additional shortcodes.

Improve the email headers to include `from` and `reply-to` headers.
Add shortcodes for '[topic-url]', '[topic-author-url]' , '[topic-whois-author-ip]' that can be used in the email body.
Make subject clearer more concise so one can more easily create email inbox filters if receiving notifications from multiple WP installs.