Fix typo in breadcrumb_classes setting

This pull-request will sanitize the option value accepted by the theme setting breadcrumb_classes by removing the trailing space.

I know this is __not backwards compatibly__, but please think about adjusting your last change to a more sane option-value. Maybe one could run a migration on updating the theme, but I am not that much into maintaining Drupal Modules. If you can lead the way, I am happy to integrate a simple migration that fixes existing database values as well.

The two commits fix the theme settings admin pane (`theme-settings.php`) and the interpretation of the value inside `template.php`

Best regards and keep up the good work,

Lennart