3271, 3441 fix share HTML, add Tumblr share, add Additional Tags to share

http://code.google.com/p/otwarchive/issues/detail?id=3441 and http://code.google.com/p/otwarchive/issues/detail?id=3271

*Adds line breaks to the share HTML to maximize compatibility with other sites
*Adds a Tumblr share button
*Adds Additional Tags to the information included in the share link

**NOTE:** Please don't merge until **after** 3274. The existing code uses the share code for the subscription e-mails, and these changes would add some unwanted spacing to the e-mails. The new email code for 3274 (pull request 1050) no longer uses the share code and thus this will not affect it.