Transating 'Logged in as <name>' instead of 'Logged in as'.

@cshold Trying to set the best example possible for designers, we should always translate whole phrases. 

I think we could even let the translator decide which words get a link to the account page here.

So use: 

      {% capture first_name %}{{ customer.first_name }}{% endcapture %}
      {{ 'layout.customer.logged_in_as_html' | t: first_name: first_name }}

And then the translation:

      "logged_in_as_html": "Logged in as <a href="/account">{{ first_name }}</a>",

That way, I can decide to translate to:

      "logged_in_as_html": "<a href="/account">My account</a>",

... if I don't like to use first_name even.