dispose of HITs

-previously could only "expire" a hit
- you can dispose of HITs which delete them entirely
prettier printing for listing hits
changes to what is posted to Ad Server (Issue #58)

- user doesn't need to post custom thanks.html and error.html templates, just the ad
- user provides a email address to contact in case of errors which the server can use
check maximum size for ad template
dispose/delete HITs on AMT and Ad server
minor bug fixes
minor bug fixes, working on disposing of hits... it is a little complicated.