Impement a way to set the per role attachment validation variables in a UI

Since D7 no longer uses the upload_* variables for per role file validation settings, we need to implement this in Contact Attach. The variables should be set on the contact_attach_admin_settings form. This form now needs a form validation handler as well to check for valid values. Also add variable deletion for all contact attach variables in the implementation of hook_uninstall(). We can no longer know the exact names of the variables, as they vary according to role ID, so we can no longer call variable_del. A db_delete('variable')->condition('name', 'contact_attach_%', 'LIKE')... should do the trick.