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 words" 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.