Add support for friendly admin emails

[fritzmg]

Currently the notification center will not send an email notification if you are using a friendly email for the administrator email address.

Similiar to #298 this PR fixes that.

Notes:

• I wasn't sure whether translations are managed on Transifex or not. I have only adjusted the English translation.
• @Toflar I changed the implementation of how the token values are added to the token collection. Is there a practical difference between

  $tokenCollection->addToken(new Token(…))

  and

  $tokenCollection->add($this->tokenDefinitionFactory->create(EmailTokenDefinition::class, …)->createToken())

  ? For simplicity in this implementation I only used the former to add the token to the collection.

[Toflar]

I wasn't sure whether translations are managed on Transifex or not. I have only adjusted the English translation.

They are not, see README.

• @Toflar I changed the implementation of how the token values are added to the token collection. Is there a practical difference between
  $tokenCollection->addToken(new Token(…))

Yes, please change back. The reason for this is that you can replace/decorate the TokenDefnitionFactory and provide your own logic for the EmailTokenDefinition and do whatever you want in createToken() then.

[fritzmg]

I see :). Will adjust both.

[fritzmg]

Done 👍

[Toflar]

Perfect, thanks @fritzmg!