Filters, search, /schedule, /persons/@me, lastModified fields, bugfixes

* Fixed: The URL field of Course is null ('url' field is already taken, renamed it to 'link')
* Fixed date input where filtering with dates is possible (now uses ISO8601 format)
* Added **/schedule** endpoint
* Added search function to persons (use q=..., "search for more word" also supported)
* Added Affiliations filter to persons (use affiliations=... parameter)
* Added buildings/<id>/rooms, which lists the rooms which are in the building with the id
* Added lastModified fields. Automatically fills at every save.
* Added **persons/@me** endpoint. As of Authentication and Session middlewares are not used by the project, it is just a demo. See comments in the code