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.
Display creation date in papers page

Diplay creattion date in paper list.

Papers can be filter by creation date (created today, yesterday, this
week, last week, this month and this year).