Tickets module

Initial commit for the tickets module. 

A ticket can be created by:

- sending a request to `/api/tickets/create`. The endpoint accepts a `publicationId ` parameter (e.g. p:Cam:1De23Ew6Ef).
- creating a new publication. The `oae-publication` module will dispatch a `created` event when the publication is created. The `oae-module` listens to the `created` event and generates a ticket afterwards.