Fix OpenID login (#416)

Fork the OpenID selector (and bascially rewrite it) due to brain-dead design that only expects one form. Additionally, i18n (it's only 1 line) has been moved to mainline adhocracy.

We can furthermore move 

- [ ] CSS 
- [ ] JavaScript
- [ ] and images

into our mainline pipeline to speed them up and get rid of the weird loading in src/adhocracy/templates/openid/form.html .