integrate branch entity-property-axel

Thanks, I've merged in on of your commits with a reworded commit message, some are already deprecated I think though. Please always use full sentences starting with upper case and ending with a point. We try to keep a polished history so hopefully the branch can be merged in.

also see http://drupal.org/node/1732726#comment-6399802

thanks, merged except for the last one:

$this->langcode->setValue($value);
}
- elseif (is_object($value)) {
+ // @TODO: Check against LanguageInterface instead of Language class when av
+ elseif ($value instanceof \Drupal\Core\Language\Language) {
$this->langcode->setValue($value->langcode);
}
else {

Do we have already an issue/concrete plans for the language interface? Else, I'd leave out the comment for now. Also it should be @todo. Then, we have to import the class always. That needs fixing in some other cases in the current code as well, e.g. \InvalidArgumentException .