all errors need to provide a email address for who to contact
changes to database schema

- no longer storing error.html and thanks.html in database
- instead user provides a email address about who to contact if there's an error
- no need to "lifetime" associated with the ad.  Ads are deleted when HITs are "disposed" on AMT
handling the correct contact_email for different routes

in case of error..
hiding experiment exchange for now
check maximum size for ad template
wrong place for this variable
minor bug fixes for SUPPORT_EMAIL variable
minor bug fix