Split ADHOCRACY_URL config variable in backend and frontend
Adjust show-discussion directive to actual functionality

This now embeds the adhocracy create-or-show-comment-listing widget,
which creates new commentables on the fly.

This can be used as the following:

    <show-discussion ng-if="metric.id" data-key="metric_{{ metric.id
}}"></show-discussion>
Merge pull request #14 from nidico/adhocracy-real-show-discussion

Adjust show-discussion directive to actual functionality