Incorrect Index updated

* incorrect index on contacts resulted in contact dupes
* added unique index on contact+type
* closes #73

* removing dupes and fixing re-ping query dealt with non-stop pings after user has responded
* closes #70

* added an 'optin' and 'unsubscribe' column to contacts table for subscription handling via email
Merge pull request #74 from ushahidi/contacts-dev

Incorrect Index updated