Validation errors and use of unsupported exclamation mark placeholders

Placeholders with exclamation mark (!placeholder) in t()-functions are no longer supported in Drupal 8: https://www.drupal.org/node/2575819

The name module uses these placeholders in various places, causing errors.

On top of that, the part of the code that checks whether all necessary components are filled in, contains an error:
$missing_components = array_diff($minimum_components, array_keys($item_components));
should be
$missing_components = array_diff(array_keys($minimum_components), array_keys($item_components));
Otherwise you get errors.

Patch included. I may have gone a bit overboard, but I replaced all !placeholders with @placeholders, I fixed the components validation error and I also changed the field-required error string to conform with the default field-required error strings.