Working with GUID and Object-Type - bugfix for API

* Bugfix for issue https://github.com/friendica/friendica/issues/1010
* Better GUID function, GUID expanded to 32 characters (the new limit of diaspora) and 30 characters for imported posts
* New schema to access posts. Its now "/display/(guid)" instead of "/display/(user)/(id)". This has the advantage that the URL of the post will always be the same between different users and even between different servers. It's one step to a changed database structure where items with the same GUID will only be stored once.