Link user posts

This adds a link for each post on a user's page to the post in its thread. The timestamp text "posted ... ago" is made into the link, in the style of... Facebook. (Perhaps there is a better place for the link?)

In the interest of DRY, we add post methods GetThreadId and GetLink to help with this.

Also, do you think the user page should show the title of the thread for each post?