Migrate to Awestruct 0.5.5

The upgrade went smooth. @hferentschik 
I only found some issue with our 404 page that I fixed. The rest looked like the previous site.

One question I have is on the best practice. Should we set versions of dependencies on `Gemfile`, or let `Gemfile.lock` be the version guardian. Of course the main dependencies like `awestruct` would have their version set in `Gemfile`
Seems there is quite a change of gems involved. Did you check the existing list against the latest awestruct I assume, right?

Btw, I think it is the right thing to remove the versions in the Gemfile. They will get locked down in Gemfile.lock.