This will allow users to send invitations to other people via email.
Each account will still need to confirm the email address if the option
is enabled.
Addresses #330, will need to allow pool operators to enable this feature
even with registrations turned off.
* Fix API Key generation not using SALT when creating hash
* This should not affect existing API keys since hashes are compared
* Fix PHP Warning for RECAPTCHA if disabled
Fixes#328