allow owners to delete their tenant/account

We've gotten a few support requests of people trying out the app asking us to delete their account. They should be able to do this themselves :)

![screen shot 2014-08-10 at 15 39 57](https://cloud.githubusercontent.com/assets/749864/3869515/2e903508-2094-11e4-81be-f8c3aa2e1da9.png)

@dkhgh do you think this is clear enough to indicate that the entire tenant/subdomain will be deleted or should we tweak the copy a bit?