Separate paper info and roles API

From now on:
 - `/papers/:paper_id/info` serves the core paper information such as
   paper name, paper creation date, paper kind, ...
 - `/papers/:paper_id/roles` serves the different roles for the paper
Merge pull request #91 from satabin/feature/cleaner-paper-api

Separate paper info and roles API
Correctly stop managed actors in dispatcher

After having sent the `Stop` message, send the `PoisonPill` message that
will actually kill the managed actors.