Removed password/key fields in {{ settings:x }}

Removed some fields from the plugin in case the user could get access
to these somehow. They shouldn't be needing these anyway. If they do
they can write a custom function for it.

Removed ga_email, ga_password, files_cf_api_key, files_cf_username,
files_s3_access_key, files_s3_secret_key, mail_smtp_pass.