Merge pull request #77 from azul/feature/3522-configurable-logfile

add config setting for logfile
Remove references to email_settings controller, which has been removed. An identities controller will replace it.
Merge pull request #78 from jessib/finish_removing_email_settings_references

Remove references to email_settings controller, which has been removed. ...
Ensure json requests get json error response on failure

Normally rails sends an html page which can't be parsed by the client.
Test the error handling of json and html responses
integration test for displaying internal server error during signup